NUTRITION OF PARASITES AND SAPROPHYTES 



consumption or tuberculosis caused by B. tuberculosus in the 

 lungs and other parts of the body, diphtheria caused by B. diph- 

 theria, lockjaw or tetanus caused by B. tetani. This last or- 

 ganism is abundant in cultivated soil and on old rusty nails. 

 When deep wounds in the flesh are caused by punctures with 

 objects carrying the germs, because of the character of the wound 

 the air is excluded. Bacillus tetanus is an anaerobe and can only 

 grow and produce the tetanus symptoms in the absence of oxygen. 

 Opening such a wound to admit air, and disinfecting it with a 

 weak solution of bichloride of mercury will prevent its action. 

 Other bacterial diseases are pneumonia, influenza or la grippe, 

 anthrax, swine plague, etc. Many of these bacteria develop 

 and excrete toxic substances called toxins, which are very 

 poisonous. These act locally on the tissues, and in many cases, 

 as in diphtheria, are carried in the blood to all parts of the 

 system and cause the fever in the patient. The bacteria them- 

 selves are in a number of cases finally checked in their growth or 

 killed by these same toxins which they excrete. This principle 

 has led to an important practice in the prevention and cure of 

 some of these diseases, i.e., by injecting what is called an antitoxin 

 into the blood. In the case of smallpox the bacteria are inocu- 

 lated into healthy cows and a mild form of the disease is developed. 

 To prevent smallpox in man some " virus " of the " cow pox " 

 is then inoculated into the system, or the person is vaccinated. 

 The result is a very mild form of the disease and the system is able 

 to resist it. But the distribution of the toxin in the system renders 

 the person immune from the disease even in a virulent form for 

 a number of years. So in the case of certain contagious diseases, 

 as in cholera, if the patient recovers he is immune from the disease 

 for a period of years. 



In the case of diphtheria the antitoxin is obtained from the 

 blood of healthy horses in the following way. The toxin is first 

 obtained from pure cultures of virulent forms of the bacillus. 

 Successive subcutaneous injections of this toxin are made in the 

 horse every 5 to 7 or 3 to 7 days for a period of about three months 

 when blood is drawn from the jugular vein of the horse, allowed 



