194 ELEMENTARY BIOLOGY 



i. The proteins of different species of animals may be very much 

 alike, so far as the tests of the chemical laboratory show, but the 

 living protoplasm can detect specific differences. Because of the 

 formation of precipitins it becomes possible to determine whether a 

 given drop of blood, for example, is of human origin or from some 

 other animal. This is often important in legal trials. 



FIG. 72. Reduction in deaths from diphtheria in New York City (Manhattan 



and Bronx) 



The numbers and rectangles on the left show the number of deaths out of every hun- 

 dred thousand of the population. The numbers on the right show how many fatalities 

 there were for every hundred cases of the disease. Note the rapid falling off in both the 

 proportion and the number of deaths after the year 1895, when antitoxin was first used 



2. In the examination of food products that contain materials from 

 various sources, it is impossible to determine, by the usual chemical 

 methods, from what organisms the materials were obtained. By means 

 of the precipitin tests, however, it is possible to find out whether a 

 given sausage, for example, contains pork or beef or horse meat. 



3. Experiments now under way in laboratories and hospitals make 

 it appear probable that this principle will have wide application in the 

 diagnosis of disease. 



224. Antitoxins. In the bodies of various plants and animals 

 are found proteins that act in a peculiar way upon the blood 

 of higher animals. They act as poisons that stimulate the 

 living cells, and especially the white blood cells, to produce 



