METHODS OF SERO-DIAGNOSIS. 205 



of diagnosis is applied to the detection of the nature of blood- 

 stains on clothing, etc., in the one case, and to the detection of 

 falsified flesh in the other. The precipitins are, like the agglu- 

 tinins, relatively thermostable, resisting heat to about the same 

 degree, and the remarks made as to the action of the agglutinins 

 apply to them as well. 



We still have to consider that class of antibodies concerned 

 in the so-called opsonic action, and which are known as Opsonins, 

 since it is thought by Wright that, by their action on the organisms 

 entering the body, these latter are rendered more susceptible to 

 ingestion by the leucocytes, by reason of their increased attrac- 

 tiveness. Metchnikoff looks on immune serum as increasing 

 phagocytic action rather by stimulation of the leucocytes than by 

 its action on the bacteria. Wright's experiments, however, led 

 him to think that these opsonins acted in the before -mentioned 

 manner on the bacteria of certain affections, and more notably 

 on staphylococci, streptococci and the bacillus of tuberculosis. He 

 also thought that these opsonins were distinct and specific anti- 

 bodies, and that their presence was absolutely necessary for 

 phagocytosis to occur. 



Some other workers think they are not a distinct form of 

 antibodies, and Lohlein pointed out that the leucocytes were capa- 

 ble of performing their phagocytic action when washed and thus 

 freed of serum altogether; but there are still others who go so 

 far as to attribute to the opsonin the possession of a combining 

 group on which their action depends, and since, after inactivation 

 by heat, the opsonic action is not restored by the addition of 

 complement, they regard them as receptors of a similar nature to 

 agglutinins and precipitins. 



Wright holds that the quantity of these opsonins in the blood 

 may be taken as a measurement of the degree of the immunity 

 of the individual towards infection by certain organisms, such as 

 those above mentioned and some others, and has 

 brought vaccine therapy into extensive use once more 

 in the case of certain bacterial infections, urging 

 that this method of treatment is of great value when 

 controlled by measurements of the opsonic index. In the hands 

 of others, however, the method has not given the results claimed 

 for it by W T right and his school. The method of examination for 

 the presence of opsonins may be briefly indicated here. It con- 

 sists in bringing into contact a suspension of leucocytes in physio- 

 logical salt solution (in which fluid these leucocytes have been 

 previously washed) with the bacteria on which their phagocytic 

 power is to be estimated, and to a part of the mixture of the 

 leucocytes and bacteria we add the serum of the subject to be 

 examined, whilst to another portion of the same mixture we add 

 the serum of a number of individuals taken to represent the 

 normal. We incubate these mixtures at 37 C for a certain time 

 and then, having made and stained films from these mixtures on 

 glass slides, we count the number of bacteria which have been 

 ingested by the leucocytes which have been mixed with the serum 



