BLACK WIDOW SPIDER — D'AMOUR ET AL. 



415 



preparations in order to overcome the individual variation which 

 exists between animals of the same species, weight, and age. In 

 order to establish the toxicity of spider venom we therefore injected 

 varying amounts into groups of 10 rats per dose. Figure 1 shows the 

 results obtained, with the amount of venom indicated both in frac- 

 tional parts per spider and in absolute weight. 



As will be noted, the average lethal dose — that is, the amount of 

 venom which will kill 50 percent of the rats — is one-fourth the venom 

 contained in the glands of one spider, or 0.032 mg. This is the amount 

 meant when the term "average lethal dose" or "equivalent of one- 

 fourth spider" is used in describing subsequent experiments. 



Table 3 



Mode of injection. — In obtaining the above toxicity curve, as well as 

 in practically all of the later work, intraperitoneal injections were 

 given. A preliminary study, the results of which are shown below, 

 indicated this type of injection to be preferable, inasmuch as the 

 amount of venom necessary to cause death was somewhat less and 

 also the length of time before death occurred was shorter when intra- 

 peritoneal injections were given. As we did not know in advance 

 how plentiful the spiders would be, we naturally made use of the 

 method which would require the least expenditure of venom, and 

 having used this method in obtaining the toxicity curve continued 

 with it in further experiments so that the results would be comparable. 



Weight of rats. — The weight of the rat is an important factor in the 

 amount of venom necessary to obtain a required result. For reasons 

 given, we used immature rats weighing between 50 and 60 grams. 

 Litters in prospect promised an adequate supply of rats of this size 

 throughout the summer months. No extensive experiment was 

 carried out to discover the ratio of venom to body weight; however, 

 table 4 gives the data on the few trials which were made. 



Type of spider. — The spiders used throughout in the work reported 

 elsewhere in this paper were mature females, as indicated by the 

 absence of any markings on the dorsal surface. (See plates.) How- 

 ever, it] seemed desirable to investigate the toxicity of immature 

 females'and of males as well. For this purpose glands from both groups 

 were obtained in the usual way and injected. The results are given 

 in table 5. 



