168 MICROBES AND TOXINS 



and the frog, kept at a low temperature, do not take tetanus and 

 retain the toxin intact in their blood for months. The tortoise, 

 which does not take tetanus either at high or low temperatures, 

 retains in its blood for months enough toxin to give tetanus to 

 mice on injecting it. The fowl also, very little sensitive to 

 tetanus, retains toxin in its blood for long periods. 



The frog, which is refractory to tetanus in winter or when 

 kept at a low temperature, takes tetanus in summer or when it 

 is kept warm in an incubator at about 30 C. At this tempera- 

 ture the poison disappears from the blood and the organs much 

 more quickly than in the cold. The course of the tetanic 

 symptoms can be interrupted at will in the frog kept in the 

 incubator by putting it again at a low temperature. In this 

 way the phenomena may be suspended as long as the chilling 

 continues ; if it is again put in the incubator the symptoms 

 recommence at the stage at which they were interrupted. In 

 the frog, fixation and response are, therefore, to a certain 

 extent dissociated, for in the cold the toxin is fixed by the cells 

 yet the disease does not appear. 



Vegetable Toxins. The bacterial toxins are vegetable 

 toxins since bacteria are microscopic plants. They have their 

 analogies in the higher plants, for example, ricin extracted from 

 the seeds of the common castor oil plant ; abrin from the 

 Abrus precatorius or jequirity ; crotin from the plant croton 

 tiglium. 



Ricin inoculated subcutaneously can kill a rabbit in a dose 

 of 0*1 mg. per kilo, body-weight; it agglutinates into masses 

 and dissolves the red corpuscles of the blood. The agglutina- 

 tion is so rapid and powerful that it is necessary to keep 

 shaking the tube in order to perceive the haemolysis. The 

 chemical nature of ricin is not exactly known ; it is not 

 absolutely certain that it is an albuminoid substance (Jacoby). 

 Abrin agglutinates the red corpuscles but is not a powerful 

 lysin. Crotin requires a dose of several centigrams per kilo, to 

 kill a rabbit. 



Toxins and Antitoxins. A fundamental difference 

 exists between the poisons of known chemical composition, 



