Part 7

At one time the writer believed that tyrotoxicon was the active agent in all samples of poisonous cheese, but more extended experimentation has convinced him that this is not the case. Indeed, this poison is rarely found, while the number of poisons in harmful cheese is no doubt considerable. There are numerous poisonous albumins found in cheese and other milk products. While all of these are gastro-intestinal irritants, they differ considerably in other respects.

In 1895 the writer and Perkins made a prolonged study of a bacillus found in cheese which had poisoned fifty people. Chemically the poison produced by this germ is distinguished from tyrotoxicon by the fact that it is not removed from alkaline solution with ether. Physiologically the new poison has a more pronounced effect on the heart, in which it resembles muscarin or neurin more closely than it does tyrotoxicon. Pathologically, the two poisons are unlike, inasmuch as the new poison induces marked congestion of the tissues about the point of injection when used upon animals hypodermically. Furthermore, the intestinal constrictions which are so uniformly observed in animals poisoned by tyrotoxicon was not once seen in our work with this new poison, although it was carefully looked for in all our experiments.

In 1898 the writer, with McClymonds, examined samples of cheese from more than sixty manufacturers in this country and in Europe. In all samples of ordinary American green cheese poisonous germs were found in greater or less abundance. These germs resemble very closely the colon bacillus, and most likely their presence in the milk is to be accounted for by contamination with bits of fecal matter from the cow. It is more than probable that the manufacture of cheese is yet in its infancy, and we need some one to do for this industry what Pasteur did for the manufacture of beer. At present the flavor of a given cheese depends upon the bacteria and molds which accidentally get into it. The time will probably come when all milk used for the manufacture of cheese will be sterilized, and then selected molds and bacteria will be sown in it. In this way the flavor and value of a cheese will be determined with scientific accuracy, and will not be left to accident.

CANNED FOODS.--As has been stated, the increased consumption of preserved foods is accountable for a great proportion of the cases of food poisoning. The preparation of canned foods involves the application of scientific principles, and since this work is done by men wholly ignorant of science it is quite remarkable that harmful effects do not manifest themselves more frequently than they do. Every can of food which is not thoroughly sterilized may become a source of danger to health and even to life. It may be of interest for us to study briefly the methods ordinarily resorted to in the preparation of canned foods. With most substances the food is cooked before being put into the can. This is especially true of meats of various kinds. Thorough cooking necessarily leads to the complete sterilization of the food; but after this, it must be transferred to the can, and the can must be properly closed. With the handling necessary in canning the food, germs are likely to be introduced. Moreover, it is possible that the preliminary cooking is not thoroughly done and complete sterilization is not reached. The empty can should be sterilized. If one wishes to understand the _modus operandi_ of canning foods, let him take up a round can of any fruit, vegetable, or meat and examine the bottom of the can, which is in reality the top during the process of canning and until the label is put on. The food is introduced through the circular opening in this end, now closed by a piece which can be seen to be soldered on. After the food has been introduced through this opening the can and contents are heated either in a water bath or by means of steam. The opening through which the food was introduced is now closed by a circular cap of suitable size, which is soldered in position.

This cap has near its center a "prick-hole" through which the steam continues to escape. This "prick-hole" is then closed with solder, and the closed can again heated in the water bath or with steam. If the can "blows" (if the ends of the can become convex) during this last heating the "prick-hole" is again punctured and the heated air allowed to escape, after which the "prick-hole" is again closed. Cans thus prepared should be allowed to stand in a warm chamber for four or five days. If the contents have not been thoroughly sterilized gases will be evolved during this time, or the can will "blow" and the contents should be discarded. Unscrupulous manufacturers take cans which have "blown," prick them to allow the escape of the contained gases, and then resterilize the cans with their contents, close them again, and put them on the market. These "blowholes" may be made in either end of the can, or they may be made in the sides of the can, where they are subsequently covered with the label. Of course, it does not necessarily follow that if a can has "blown" and been subsequently resterilized its contents will prove poisonous, but it is not safe to eat the contents of such cans. Reputable manufacturers discard all "blown" cans.

Nearly all canned jellies sold in this country are made from apples. The apples are boiled with a preparation sold under the trade name "tartarine." This consists of either dilute hydrochloric or sulphuric acid. Samples examined by the writer have invariably been found to consist of dilute hydrochloric acid. The jelly thus formed by the action of the dilute acid upon the apple is converted into quince, pear, pineapple, or any other fruit that the pleasure of the manufacturer may choose by the addition of artificial flavoring agents. There is no reason for believing that the jellies thus prepared are harmful to health.

Canned fruits occasionally contain salicylic acid in some form. There has been considerable discussion among sanitarians as to whether or not the use of this preservative is admissible. Serious poisoning with canned fruits is very rare. However, there can be but little doubt that many minor digestive disturbances are caused by acids formed in these foods. There has been much apprehension concerning the possibility of poisoning resulting from the soluble salts of tin formed by the action of fruit acids upon the can. The writer believes that anxiety on this point is unnecessary, and he has failed to find any positive evidence of poisoning resulting from this cause.

There are two kinds of condensed milk sold in cans. These are known as condensed milk "with" and "without" sugar. In the preparation of the first-mentioned kind a large amount of cane sugar is added to condensed milk, and this acting as a preservative renders the preparation and successful handling of this article of food comparatively easy. On the other hand, condensed milk to which sugar has not been added is very liable to decomposition, and great care must be used in its preparation. The writer has seen several cases of severe poisoning that have resulted from decomposed canned milk. Any of the galactotoxicons (milk poisons) may be formed in this milk. In these instances the cans were "blown," both ends being convex.

One of the most important sanitary questions in which we are concerned to-day is that pertaining to the subject of canned meats. It is undoubtedly true that unscrupulous manufacturers are putting upon the market articles of this kind of food which no decent man knowingly would eat, and which are undoubtedly harmful to all.

The knowledge gained by investigations in chemical and bacteriological science have enabled the unscrupulous to take putrid liver and other disgusting substances and present them in such a form that the most fastidious palate would not recognize their origin. In this way the flesh from diseased animals and that which has undergone putrefactive changes may be doctored up and sold as reputable articles of diet. The writer does not believe that this practice is largely resorted to in this country, but that questionable preservatives have been used to some extent has been amply demonstrated by the testimony of the manufacturers of these articles themselves, given before the Senate committee now investigating the question of food and food adulterations. It is certainly true that most of the adulterations used in our foods are not injurious to health, but are fraudulent in a pecuniary sense; but when the flesh of diseased animals and substances which have undergone putrefactive decomposition can be doctored up and preserved by the addition of such agents as formaldehyde, it is time that the public should demand some restrictive measures.

WIRELESS TELEGRAPHY.

BY PROF. JOHN TROWBRIDGE,

DIRECTOR OF JEFFERSON PHYSICAL LABORATORY, HARVARD UNIVERSITY.

I never visit the historical collection of physical apparatus in the physical laboratory of Harvard University without a sense of wonderment at the marvelous use that has been made of old and antiquated pieces of apparatus which were once considered electrical toys. There can be seen the first batteries, the model of dynamo machines, and the electric motor. Such a collection is in a way a Westminster Abbey--dead mechanisms born to new uses and a great future.

There is one simple piece of apparatus in the collection, without which telephony and wireless telegraphy would be impossible. To my mind it is the most interesting skeleton there, and if physicists marked the resting places of their apparatus laid to apparent rest and desuetude, this merits the highest sounding and most suggestive inscription. It is called a transformer, and consists merely of two coils of wire placed near each other. One coil is adapted to receive an electric current; the other coil, entirely independent of the first, responds by sympathy, or what is called induction, across the space which separates the coils. Doubtless if man knew all the capabilities of this simple apparatus he might talk to China, or receive messages from the antipodes. He now, by means of it, analyzes the light of distant suns, and produces the singular X rays which enable him to see through the human body. By means of it he already communicates his thoughts between stations thousands of miles apart, and by means of its manifestations I hope to make this article on wireless telegraphy intelligible. My essay can be considered a panegyric of this buried form--a history of its new life and of its unbounded possibilities.

For convenience, one of the coils of the transformer is placed inside the other, and the combination is called a Ruhmkorf coil. It is represented in the accompanying photograph (Fig. 1), with batteries attached to the inner coil, while the outer coil is connected to two balls, between which an electric spark jumps whenever the battery circuit is broken. In fact, any disturbance in the battery circuit--a weakening, a strengthening, or a break--provided that the changes are sudden, produces a corresponding change in the neighboring circuit. One coil thus responds to the other, in some mysterious way, across the interval of air which separates them. Usually the coils are placed very near to each other--in fact, one embraces the other, as shown in the photograph.

The coils, however, if placed several miles apart, will still respond to each other if they are made sufficiently large, if they are properly placed, and if a powerful current is used to excite one coil. Thus, by simply varying the distance between the coils of wire we can send messages through the air between stations which are not connected with a wire. This method, however, does not constitute the system of wireless telegraphy of Marconi, which it is the object of this paper to describe. Marconi has succeeded in transmitting messages over forty miles between points not connected by wires, and he has accomplished this feat by merely slightly modifying the disposition of the coils, thus revealing a new possibility of the wondrous transformer. If the reader will compare the following diagram (Fig. 2) with the photograph (Fig. 1), he will see how simple the sending apparatus of Marconi is.

S is a gap between the ends of one coil, across which an electric spark is produced whenever the current from the batteries B flowing through the coil C is broken by an arrangement at D. This break produces an electrical pulsation in the coil C', which travels up and down the wire W, which is elevated to a considerable height above the ground. This pulsation can not be seen by the eye. The wire does not move; it appears perfectly quiescent and dead, and seems only a wire and nothing more. At night, under favorable circumstances, one could see a luminosity on the wire, especially at the end, when messages are being transmitted, by a powerful battery B.

It is very easy to detect the electric lines which radiate from every part of such a wire when a spark jumps between the terminals S of the coil. All that is necessary to do is to pass the wire through a sensitive film and to develop the film. The accompanying photograph (Fig. 3) was taken at the top of such a wire, by means of a very powerful apparatus at my command. When the photograph is examined with a microscope the arborescent electric lines radiating from the wire, like the rays of light from a star, exhibit a beautiful fernlike structure. These lines, however, are not chiefly instrumental in transmitting the electric pulse across space.

There are other lines, called magnetic lines of force, which emanate from every portion of the vertical wire W just as ripples spread out on the surface of placid water when it is disturbed by the fall of a stone. These magnetic ripples travel in the ether of space, and when they embrace a neighboring wire or coil they produce similar ripples, which whirl about the distant wire and produce in some strange way an electrical current in the wire. These magnetic pulsations can travel great distances.

In the photographs of these magnetic whirls, Fig. 4 is the whirl produced in the circuit C' by the battery B (Fig. 2), while Fig. 5 is that produced by electrical sympathy, or as it is called induction, in a neighboring wire. These photographs were obtained by passing the circuits through the sensitive films, perpendicularly to the latter, and then sprinkling very fine iron filings on these surfaces and exposing them to the light. In order to obtain these photographs a very powerful electrical current excited the coil C (Fig. 2), and the neighboring circuit W' (Fig. 5) was placed very near the circuit W.

When the receiving wire is at the distance of several miles from the sending wire it is impossible to detect by the above method the magnetic ripples or whirls. We can, however, detect the electrical currents which these magnetic lines of force cause in the receiving wire; and this leads me to speak of the discovery of a remarkable phenomenon which has made Marconi's system of wireless telegraphy possible. In order that an electrical current may flow through a mass of particles of a metal, a mass, for instance, of iron filings, it is necessary either to compress them or to cause a minute spark or electrical discharge between the particles. Now, it is supposed that the magnetic whirls, in embracing the distant receiving circuit, cause these minute sparks, and thus enable the electric current from the battery B to work a telegraphic sounder or bell M. The metallic filings are inclosed in a glass tube between wires which lead to the battery, and the arrangement is called a coherer. It can be made small and light. Fig. 6 is a representation in full size of one that has been found to be very sensitive. It consists of two silver wires with a few iron filings contained in a glass tube between the ends of the wires. It is necessary that this little tube should be constantly shaken up in order that after the electrical circuit is made the iron filings should return to their non-conducting condition, or should cease to cohere together, and should thus be ready to respond to the following signal. My colleague, Professor Sabine, has employed a very small electric motor to cause the glass tube to revolve, and thus to keep the filings in motion while signals are being received. Fig. 7 shows the arrangement of the receiving apparatus.

The coherer and the motor are shown between two batteries, one of which drives the motor while the other serves to work the bell or sounder when the electric wire excites the iron filings. In Fig. 2 this receiving apparatus is shown diagrammatically. B is the battery which sends a current through the sounder M and the coherer N when the magnetic whirls coming from the sending wire W embrace the receiving wire W'.

The term wireless telegraphy is a misnomer, for without wires the method would not be possible. The phenomenon is merely an enlargement of one that we are fully conscious of in the case of telegraph and telephone circuits, which is termed electro-magnetic induction. Whenever an electric current suddenly flows or suddenly ceases to flow along a wire, electrical currents are caused by induction in neighboring wires. The receiver employed by Marconi is a delicate spark caused by this induction, which forms a bridge so that an electric current from the relay battery can pass and influence magnetic instruments.

Many investigators had succeeded before Marconi in sending telegraphic messages several miles through the air or ether between two points not directly connected by wires. Marconi has extended the distance by employing a much higher electro-motive force at the sending station and using the feeble inductive effect at a distance to set in action a local battery.

It is evident that wires are needed at the sending station from every point of which magnetic and electric waves are sent out, and wires at the receiving station which embrace, so to speak, these waves in the manner shown by our photographs. These waves produce minute sparks in the receiving instrument, which act like a suddenly drawn flood gate in allowing the current from a local battery to flow through the circuit in which the spark occurs, and thus produce a click on a telegraphic instrument.

We have said that messages had been sent by what is called wireless telegraphy before Marconi made his experiments. These messages had also been sent by induction, signals on one wire being received by a parallel and distant wire. To Marconi is due the credit of greatly extending the method by using a vertical wire. The method of using the coherer to detect electric pulses is not due, however, to Marconi. It is usually attributed to Branly; it had been employed, however, by previous observers, among whom is Hughes, the inventor of the microphone, an instrument analogous in its action to that of the coherer. In the case of the microphone, the waves from the human voice shake up the particles of carbon in the microphone transmitter, and thus cause an electrical current to flow more easily through the minute contacts of the carbon particles.

The action of the telephone transmitter, which also consists of minute conducting particles in which a battery terminals are immersed, and the analogous coherer is microscopic, and there are many theories to account for their changes of resistance to electrical currents. We can not, I believe, be far wrong in thinking that the electric force breaks down the insulating effect of the infinitely thin layers of air between the particles, and thus allows an electric current to flow. This action is doubtless of the nature of an electric spark. An electric spark, in the case of wireless telegraphy, produces magnetic and electric lines of force in space, these reach out and embrace the circuit containing the coherer, and produce in turn minute sparks. _Similia similibus_--one action perfectly corresponds to the other.

The Marconi system, therefore, of what is called wireless telegraphy is not new in principle, but only new in practical application. It had been used to show the phenomena of electric waves in lecture rooms. Marconi extended it from distances of sixty to one hundred feet to fifty or sixty miles. He did this by lifting the sending-wire spark on a lofty pole and improving the sensitiveness of the metallic filings in the glass tube at the receiving station. He adopted a mechanical arrangement for continually tapping the coherer in order to break up the minute bridges formed by the cohering action, and thus to prepare the filings for the next magnetic pulse. The system of wireless telegraphy is emphatically a spark system strangely analogous to flash-light signaling, a system in which the human eye with its rods and cones in the retina acts as the coherer, and the nerve system, the local battery, making a signal or sensation in the brain.