438 Br. G. Sims Woodhead [Feb. 8, 



immunity, and an " artificial " antitoxic serum, the cells are stimu- 

 lated by the introduction into the body of artificially prepared toxine. 

 The cells acted upon by the toxine elaborate the protective fluid, 

 which is thrown into and accumulates in the blood. This substance 

 may act in one of several, or even in several ways. (1) It may 

 directly antagonise the diphtheria toxine, and may thus prevent the 

 paralysing action of these poisons on the scavenging cells or phago- 

 cytes, as they are called ; these, left free to perform their proper 

 functions, can deal with the foreign elements that have got into the 

 blood, and also with the bacilli at the seat of the local attack, for, as 

 has been pointed out by several foreign observers, and by Buffer in 

 this country, immediately beneath the layer of bacilli in the false 

 membrane there is usually a very considerable accumulation of 

 leucocytes, especially in those cases in which recovery ultimately 

 takes place. (2) The antitoxic substances may act on the bacilli, 

 inhibiting their growth and interfering with their power of producing 

 toxines. This, of course, can ouly be a local action should it play 

 any part in the process. (3) These substances may act directly on 

 the cells of the blood, lymph, and tissues, so stimulating and 

 strengthening them that they are able to perform those functions above 

 mentioned. It is at present difficult to state which of these pro- 

 cesses is the one, or the most important, in protecting or curing the 

 patient, and it may be that all play a part. It may be that the 

 tissue cells, when acted upon by the specific diphtheria poison, 

 become so modified that they are enabled to produce or secrete a 

 substance which directly antagonises the action of that poison. This 

 substance, thrown into the blood, remains there for some time, rapidly 

 accumulates as larger and larger doses of the poison are thrown in, 

 neutralising the poison, whose power of doing damage to the tissues 

 is thus held in check, but remaining for some time after the toxine 

 has disappeared ; or this antitoxic substance, reacting upon the cells, 

 may render them less susceptible to the action of the toxine. 



The earlier immunising experiments were naturally performed 

 upon the smaller animals, such as rabbits. Then Behring used sheep, 

 and after various other animals had been tried, the horse was selected 

 by Eoux and Nocard, and Aronson, as perhaps the best of all animals 

 from which to obtain antitoxic serum. In the first place, he is com- 

 paratively insusceptible to the action of the diphtheria bacillus — even 

 comparatively large doses of living bacilli may be injected under the 

 skin without producing anything more than a slight local swelling 

 and a rise of temperature. It has also been found that horse serum, 

 when injected, produces little or no change in the healthy human 

 subject — that is, the serum seems to mix perfectly well with human 

 blood plasma, and there is comparatively little danger of the extra 

 serum being excreted by the kidneys in the form of albumen. This 

 is a most important point, and one that no doubt influenced Eoux and 

 Nocard in their selection of the horse as an animal from which 

 to obtain immunised serum. Beyond this, however, the blood, when 



