520 GENERAL CONSIDERATIONS 



toxin. This may be introduced into the blood of a horse and the horse, 

 in response to its presence there, will manufacture an antitoxin. The 

 serum from the blood of the horse containing both the toxin and antitoxin 

 may then be injected into the body of a person and will not only confer 

 immunity but will tend to stop the disease if it has already been initiated. 

 The same type of procedure is followed in the case of scarlet fever, but in 

 tetanus the antitoxin alone is introduced. 



Many other toxins as well as infective organisms may be combated 

 in the body by the development of an appropriate antitoxin, which when 

 injected protects the body from the effect of such agents. 



553. Anaphylaxis and Allergy. — Anaphylaxis may be defined as an 

 exaggerated irritability of the body with respect to some foreign 

 substance. It may follow a case of mild poisoning by the substance con- 

 cerned and is associated vnih the eating of a great many foods, particu- 

 larly proteins and sea foods. A person may have eaten such a food 

 freely and without evil effects until, under certain conditions, poison- 

 ing occurs. If thereafter, whenever the food is taken, the body shows a 

 pronounced reaction, a case of anaphylaxis exists. Allergy is a similar 

 exaggerated susceptibility to contact with dust, the pollen of plants, and 

 hairs or other particles from the bodies of animals. Hay fever is such a 

 condition. The word allergy is sometimes used in a more general sense 

 to include anaphylaxis and immunity, thus referring to any altered 

 response of the body to foreign substances of any kind. 



554. Maintenance of Health in Human Beings. — Many of the condi- 

 tions which are necessary to maintain the body in a state of health may be 

 inferred from statements made earlier in this chapter. The field of 

 investigation which deals with the effect of conditions wdthin the body 

 upon health is called hygiene; when conditions outside the body are 

 involved, it is spoken of as sanitation. Preventive medicine covers in 

 general both fields. 



Always in considering the maintenance of health allowances must 

 be made for the effect of routine. The body forms habits relating to 

 all procedures connected with hygiene and these have the same control 

 over the body, when once formed, as do all habits. In changing in any 

 way his mode of living a person has to consider the adjustment which the 

 body can make. This power of adjustment is great in youth but dimin- 

 ished rapidly in old age, when changes of any kind have to be gradually 

 brought about. 



