ON THE NATURE OF TOXINS 55 



animals. These facts lead us to the belief that the exotoxins are, 

 at any rate, allied to the proteids, and form with the enzymes a 

 group of the substances of peculiar composition. 



We have referred above to ricin as a substance once thought 

 to be of definite proteid nature, and a few facts may be given 

 concerning this substance, which is closely allied in every way 

 to the bacterial toxins, and which may be taken as a type of the 

 vegetable toxins or phytotoxins. It occurs in the seeds of various 

 species of Ricinus, and was formerly regarded as being a proteid, 

 since, like the bacterial toxins, it is carried down mechanically 

 with proteid precipitates. Thus Stillmarck regarded it as a globulin, 

 since he prepared it from the seeds by a process which was adapted 

 to the separation of those substances (solution in 10 per cent. NaCl, 

 precipitation with sodium or magnesium sulphate, and dialysis). 

 But Jacoby thought he had succeeded in separating it entirely 

 from its proteid accompaniment, making use of the fact that when 

 a mixture of ricin and the other substances present in the seeds 

 are acted on by trypsin, the active principle is acted on but slightly, 

 if at all ; the ricin itself, in a pure state, is readily digested by 

 trypsin, like the other toxins. Jacoby digested an extract of 

 castor-oil seeds for five weeks, and then added enough ammonium 

 sulphate to render the fluid 60 per cent, saturated, and ricin was 

 thrown down in an almost pure state ; it was purified by repreci- 

 pitation, and then found not to give any of the proteid reactions, 

 though it retained the characteristic toxic properties of the sub- 

 stance. Quite recently, however, Osborne, Mendel, and Harris 

 obtained ricin in a very pure form, and found it to be either 

 proteid in nature or at least inseparably associated with coagulable 

 albumin ; its toxicity was removed by tryptic digestion or heat 

 coagulation. Its great potency ( Ttr Vo- m g r - being a lethal dose 

 per i kilo of rabbit) suggests that the substance which they 

 prepared was really pure. 



Ricin resembles the bacterial toxins in the following points : 

 It has a period of incubation ; it gives rise to an antitoxin when 

 suitably administered ; it is extraordinarily potent, the lethal dose 

 per kilo of weight (in rabbits) being a minute fraction of a 

 gramme ; it is destroyed by boiling ; and it is much less potent on 

 ingestion than on injection. Its main toxic properties are fever, 

 loss of weight, albuminuria, haematuria, and haemorrhage from 

 the intestine ; death occurs in about twenty-four hours with acute 

 nervous symptoms. It has a most interesting and characteristic 





