HEALTH AND DISEASE 339 



theria and pneumonia, the security given by the antitoxin 

 is only temporary. 



Certain animals are known to be subject to some of the 

 same diseases which attack human beings, or to be suscepti- 

 ble to them when the particular poisons are introduced into 

 their systems. Other animals cannot be made to " take " 

 certain infectious diseases, even when the specific germs 

 and toxins are injected into their circulations. They are 

 said to be " naturally immune " to those diseases, that is, 

 an antitoxin is supplied by nature in their blood serum 

 for the germs or toxins of those diseases. Other animals 

 are rendered immune to certain diseases by having experi- 

 enced them. 



Advantage has been taken of this knowledge respecting 

 animals for the benefit of man. In several cases the anti- 

 toxic substances in the blood of animals immune to cer- 

 tain diseases have been separated out and injected in 

 minute quantities into the veins of human subjects suffer- 

 ing from- the particular infection. The proportion of 

 recoveries when the antitoxins are used under proper 

 safeguards is increasingly and encouragingly large. 



489. Vaccination for smallpox was the first great dis- 

 covery in this direction. By means of it smallpox, which 

 was once the great scourge of the human race, as com- 

 mon as measles or whooping cough is now, has become 

 comparatively rare. The use of the diphtheria antitoxin, 

 which is derived from the blood serum of a horse which 

 has been innoculated with the diphtheria germ, is fast 

 becoming general, and we may hope to see diphtheria 

 that terror of childhood disappear with the advance 

 of beneficent science. 



The greatest destroyer of human life which now remains 

 is consumption, tuberculosis in its varied forms, and 



