EXPERIMENT STATION BULLETINS. 311 



germ in its weakened condition by simply passing it through a series of animals — 

 from the most susceptible to the least susceptible. This action of disease-producing 

 bacteria should always be borne in mind to correctly formulate opinions; it is never- 

 theless too frequently overlooked. Tlie guinea pig is susceptible to the weak form 

 of the tubercle bacillus, which in its weak form may not be capable of producing 

 tuberculosis in a strong man. What conclusions should be reached? Man cannot 

 be used to determine the exact knowledge to make our logical chain complete. We 

 know that a strong man is susceptible to tuberculosis at times and we know that some 

 men seem to be predisposed to tuberculosis. I say we know, because these are state- 

 ments generally accepted by careful observers. The next statement may require 

 demonstration. Tubercle bacilli coming from one source may be much more virulent 

 than those coming from another source, whether in man or animal. To demonstrate 

 this the author took material selected from two patients, one a case of very long 

 standing, and the other a rapidly progressing case. While it was impossible to secure 

 equal amoiuits, so far as tlie number of bacilli was concerned, to make it approach 

 equality, an estimate of the number of germs determined was used as a basis to 

 proportion the amounts. With these determined proportions guinea pigs were inocu- 

 lated. The animals inoculated with material from the case of long standing survived 

 several weeks longer than the animals inoculated from the other case. Experiments 

 repeated with tuberculous material taken from cattle gave similar results. These con- 

 clusions accord with the general accepted view. What conclusion shall be reached? 

 1 repeat, in the face of such facts. If fifty glasses of water were placed before a 

 thirsty man and one contained poison, to the man's knov/ledge, there is no doubt that 

 he would consider his thirsty condition before he drank, if he drank at all. So it is 

 in rx|ieriments witli guinea pigs: they tell us that there is danger, but do not tell 

 us how great that danger is. The bacteriologist can therefore indicate danger by 

 his simple inoculation of a guinea pig, but cannot indicate the amount of danger by 

 that simple inoculation. 



That the disease of tuberculosis is contagious has long been accepted by scientists, 

 but there are those who still doubt the trutl\ of this statement, even among phy- 

 sicians. It is not my purpose to justify the attitude of scientists, but rather to 

 repeat some of the evidence used in establishing this statement. What has been 

 said relative to guinea pigs as conclusive experimental animals will appear constantly 

 in the proof which is about to be given, and instead of being confined to guinea pigs it 

 is applicable to various other animals. 



The classic experiments of Gerlach, the director of the Berlin Veterinary School, 

 come down to us as the first crucial tests made upon the infectiousness of tuberculous 

 material. Inasmuch as these experiments were made in 1860, thirteen years before 

 Koch discovered the tubercle bacillus, there may be cause for chagrin on our part to 

 acknowledge that the conditions which control tuberculosis have not become better 

 known thirty years later. Gerlach took some tuberculous nodules from a tuberculous 

 cow and placed them underneath the skin of a goat one year old. Three weeks after 

 inoculation, tubercles as huge as walnuts appeared at the point of inoculation. Six 

 months after inoculation the disease had reached the pleural cavity and attacked the 

 bronchial glands and the lungs. Again, a healthy and well nourished calf, eight days 

 old, was fed with milk from a cow the last fifty days of her life. Fifty days from the 

 time of the last feeding, or one hundred days from the commencement, the calf was 

 killed. Tuberculosis had developed to a high degree. Tlie pleura, bronchial glands, 

 lungs, and mesenteric glands showed tubeicles of good size, manj' of them as large as 

 walnuts. In an eight months' lamb, fed with milk from the same cow, incipient 

 tuberculosis had developed when killed three months after. A pig, six to eight weeks 

 old, was fed for twehe days with millc from the same cow as above, and was killed 

 thirty days after. Tlu' lungs, broncliial glands and mesenteric glands were badly 

 afTected with tuberculosis. These experiments of Gerlacli (1874), following upon those 

 of Villemin's (1865), demonstrated conclusively, even in the light of our present 

 knowledge, that tuberculosis in a cow could be conveyed to other animals by inocula- 

 tion and by feeding. Villemin's work also showed tliat tuberculosis of the human 

 subject could be conveyed to lower animals by inoculation of tuberculous sputum. 

 His methods were similar to those of Gerlach. Tappeiner succeeded in inducing the 

 disease in rabbits, guinea pigs and dogs by causing them to inhale powdered and 

 suspended tuberculous sputum. Tlie laboratory servant wliile conducting these experi- 

 ments also fell a victim to this disease. Cornet has found tubercle bacilli in dust. 

 Sputum becoming dry, soon is pulverized and escapes into the air. Out of 392 sam- 

 ples of dust gathered from asylums, prisons, liospitals where consumptives are found, 

 Cornet determined 5!) to contain tubercle bacilli. 



