546 IMMUNITY 



phenomena, as in the case of agglutination, are met with. If the anti- 

 serum be heated to a temperature of 75 C. for some time it acquires 

 inhibitory properties, so that when added to a mixture of serum and anti- 

 serum which would otherwise give a precipitate, this no longer occurs. 

 Some observers consider that this is due to the presence of " precipitoid " 

 in the heated anti-serum ; but the observations of Welsh and Chapman 

 show that this view is not in accordance with the facts, and indicate that 

 the inhibition is related to a specific solvent action which the heated anti- 

 serum lias on the precipitate. They have also shown that the main mass 

 of the precipitate is furnished by the anti-serum (precipitin). and not as 

 is usually supposed by the precipitin throwing down the protein of the 

 homologous serum ; this result is of high importance in connection with 

 the action of anti-substances in general. The precipitin reaction is specific 

 in the sense explained above. It is always most marked towards the 

 serum of the species used in the immunisation ; but while this is so, 

 there may also be a slight reaction towards animals of allied species. An 

 anti-human serum, for example, gives the maximum reaction with human 

 serum, but also a slight reaction with the serum of monkeys, especially of 

 anthropoid apes ; it, however, gives no reaction with the serum of other 

 animals. The precipitin test has thus come to be employed as a means of 

 differentiating human from other bloods. Another interesting phenomenon 

 is what is known as the " deviation of complement," which is produced by 

 the combination of the two substances in the serum and anti-serum respect- 

 ively. If mixtures be made according to the above method, and then a small 

 quantity of complement, say fresh guinea-pig serum, be added, it will be 

 found that the complement becomes absorbed, as may be shown by sub- 

 sequently adding a test amount of sensitised red blood corpuscles. This 

 deviation phenomenon is even a more delicate reaction than the precipitin 

 test, it being often possible to demonstrate by its use from a tenth to a 

 hundredth of the smallest amount of serum which will give a perceptible 

 precipitate ; it also is specific within the same limits. 1 



Therapeutic Effects of Anti-Sera. As will have been gathered, 

 the chief human diseases treated by anti-sera are diphtheria, 

 tetanus, streptococcus infection, pneumonia, dysentery, plague, 

 and snake bite. Of the results of such treatment most is known 

 in the case of diphtheria. Here a very great diminution in the 

 mortality has resulted. The diphtheria antitoxin came into 

 general use about October 1894, and the statistics published by 

 Eehring towards the end of 1895 indicated results which have 

 since been confirmed. In the Berlin Hospitals the average 

 mortality for the years 1891-93 was 36 '1 per cent., in 1894 it 

 was 21 '1 per cent., and in January-July 1895, 14'9 per cent. The 

 objection that in some epidemics a very mild type of disease 

 prevails is met by the fact that similar diminutions of mortality 

 have occurred all over the world. Loddo collected the results 

 of 7000 cases in Europe, America, Australia, and Japan, in 



1 For an account of precipitins, vide Nuttall, "Blood Immunity and 

 Relationships," Cambridge, 19*04 ; and of complement deviation, Muir and 

 Martin, Journ. of Hyg. (1906), vi. p. 265. 



