COMMUNICABLE DISEASES. 221 



Technic for Performing the Reaction. Into a test-tube place 0.2 c.c. 

 of the antigen, 0.2 c.c. of the patient's serum (antibody), and o.i c.c. 

 of the complement. Incubate at 37 C. for three-quarters of an hour and 

 then add i.o c.c. of the solution of hemolytic serum, containing two minimal 

 doses and i.o c.c. of the 5 per cent, suspension of lamb's blood-corpuscles. 

 Incubate the whole for two hours, place in the refrigerator over night, and 

 then note if hemolysis has occurred. If the antibody of syphilis is present in 

 the suspected blood serum, hemolysis will not occur because the complement 

 is "fixed" to the immune body by the aid of the antigen and the reaction is 

 positive. Should the suspected blood serum not contain the specific antibody, 

 hemolysis will occur because there is no immune body to "fix" the com- 

 plement, therefore causing the hemolytic amboceptor (hemolytic serum), 

 by the aid of the red corpuscles, to fix the complement, producing hemolysis 

 and the reaction is then negative. 



The substances employed are subject to many external influences, and 

 it is, therefore, necessary to control their action. The controls made are 

 necessary in order to demonstrate that none of the employed substances 

 alone "fix" the complement, and that the occurrence of either a positive or 

 a negative reaction, when testing a suspected serum, is due to and dependent 

 upon the fixation or non-fixation of the complement by means of the immune 

 body. 



The quantity of antigen used for the reaction may have to be either 

 increased or decreased. The controls will indicate when a change is required 

 and the proper quantity necessary is determined by the method given under 

 the preparation of the antigen. 



There are many other communicable diseases as measles, mumps, 

 scarlet fever, and whooping cough, besides the diseases due to the attacks of 

 higher parasites, as itch, trichinosis, tapeworm, roundworm, liver flukes, 

 hookworm, etc., which we will, however, not discuss more fully. The sug- 

 gestions given under the diseases described will also apply, in a measure, 

 to other communicable diseases. Summed up briefly, preventive medicine, 

 direct and indirect, consists of giving heed to the following. 



1. Living in accord with the most approved methods of hygiene. This 

 is direct preventive medicine. 



2. Treating disease in accord with the most approved modern methods. 

 This is indirect preventive medicine because it protects the well against 

 infection from the sick. 



The following table of communicable diseases giving the average period 

 of incubation (also known as latent period), the primary cause, nature of 

 communicability and principle carriers or sources of infection, will be 

 found useful. 



