MICROPHYTOLOGY 137 



the subject is proof against further attacks. A second 

 attack of small-pox is very rare. Persons who have had 

 tuberculous glands in youth seldom contract tuberculosis of 

 the lungs. Typhoid fever, scarlet fever, chicken-pox, etc., 

 may attack a second time, but the second attack is not 

 likely to do much harm. For more than a century people 

 preferred to inoculate themselves with small-pox, securing a 

 mild attack when the system was not predisposed to the 

 disease, rather than run the risk of an attack under unfa- 

 vourable circumstances; but <( Variolation" was prohib- 

 ited by Act of Parliament in 1840 because the inoculated 

 person was a focus of the disease. Although he might 

 secure a mild attack for himself, he was just as liklyasany 

 other small-pox patient to distribute the disease in a virulent 

 form to his attendants. In 1796 Jenner made the great 

 discovery that inoculation with small-pox which had passed 

 through the body of a cow (an animal which is compara- 

 tively immune), and had thus become attenuated, produced 

 a mild attack of "cow-pox," which is a perfect protection 

 against small-pox, although the person so affected cannot 

 spread the unattenuated disease. 



In the treatment of hydrophobia the virus is attenuated in 

 a different way. The spinal cord of a rabbit which has 

 died of the disease is dried. A broth-culture is made from 

 the dried cord and the patient is inoculated with this. He 

 is thus rendered immune before the attack of hydrophobia 

 has had time to supervene. Fortunately, a long interval 

 elapses between the bite and the development of the disease. 

 The same treatment would probably be applicable to lock- 

 jaw if it were possible to ascertain that the germs had been 

 introduced into a wound. Cholera is anticipated and dis- 

 armed by inoculating a person with a culture of the cholera- 

 spirillum which has been weakened by cultivation in broth or 

 agar. Plague is stayed by introducing into the system of 

 those who have not yet been attacked a sufficient dose of 

 plague-toxins prepared from a culture of the bacillus which 



