62 Transactions Tennessee Academy of Science 



formity to Mendel's law, thus placing the hereditary nature of the 

 disease resistance beyond doubt. The same must be true in the case 

 of animals, including man. If alternating columns of unvaccinated 

 Mexicans and Anglo-Saxons should be equally exposed to a viru- 

 lent type of small pox, a photograph of the columns similarly placed 

 after the passing of the epidemic would very probably greatly re- 

 semble the clover experiment shown a moment ago. There is little 

 doubt, however, that plant pathologists are inclined to lay more 

 stress on heredity of immunity and susceptibility to disease than are 

 human pathologists. A plant pathologist is then rather inclined to 

 predict that in the next few decades the medical profession will lay 

 more stress on heredity of immunity than they do at the present time. 



In the study of the physiology of resistance and immunity the 

 animal pathologists are far in advance of plant pathologists, thanks 

 to the brilliant succession of researches led by Pasteur in the last 

 century. 



Let us for a short time consider some of these results. I have not, 

 of course, the time or the knowledge of the subject to give you any 

 other than a very inadequate survey of the question, and will only 

 call your attention to certain phases of it. 



To Metchnikoff is due credit for the discovery of phagocytosis, 

 by means of which foreign bodies in the blood stream, such as 

 pathogenic bacteria, are engulfed by an amoeboid movement of the 

 white blood corpuscles and destroyed by a process of digestion not 

 unlike the regular act of feeding by the one-celled amoeba. For 

 some time this was thought to be the only means of defense against 

 infection possessed by the human or animal body. It was soon 

 found, however, that there are produced substances or bodies in the 

 blood serum which are able to destroy bacteria or to render them 

 harmless without the intervention of the phagocytes. It was also 

 shown that the phagocytes themselves are often powerless to attack 

 bacteria in the absence of certain specific sensitizers in the serum, 

 called opsonins. Of the wonderful advance in medical science due 

 to all these brilliant discoveries, to which Behring, Koch, Ehrlich, 

 Wright, and others have contributed, the world knows. 



To make a long story short, there are produced in some cases 

 bodies that directly neutralize the toxic products of the bacteria, the 

 toxins. These bodies are called anti-toxins. In other cases special 

 serum constituents are found which attack the invading bacteria di- 

 rectly and destroy ihem. These were termed bacleriolysins. Certain 



