360 PRINCIPLES OF GENERAL PHYSIOLOGY 



Poisons. Many interesting substances of this class are to be met with, 

 sometimes produced for the capture of food, sometimes for defensive or offensive 

 purposes against enemies. The rnason wasp injects, with its sting, a toxic 

 substance into the nerve ganglia of its prey, spiders. This produces paralysis, 

 while the spiders still remain living and ready for food when wanted. The wasp, 

 in fact, deposits an egg in proximity to the paralysed spider, so that, when the 

 grub hatches, it finds fresh food, living but powerless, ready for it to consume 

 Warburton's "Manual," 1912, p. 124). 



Henze (1913) shows that the poison used by cephalopods to paralyse their 

 prey, especially crabs, can be extracted by alcohol from the posterior " salivary 

 glands. The active substance is found to be para-hydroxy-phenylethvlaiiiiiie, 

 which was shown by Barger and Walpole (Barger and Dale, 1910, p. 31) to be 

 produced from tyrosine, by removal of CO.,, in the putrefaction of meat. The 

 chemical relationship of this substance to adrenaline is of interest in view of 

 the production of this latter in the organisms. Thus : 



OH OH 



H / \ H H r \ OH 



HN/ H H JH 



CH 2 HCOH 



CH 2 CH 2 



NH, CH :t NH 



Para-hydroxy-phenylethylamine. Adrenaline. 



It is also interesting to note that Sepia, one of the cephalopods, makes use of 

 tyrosine in another way, to form the black pigment of its inky secretion, as 

 mentioned above. 



Salivary glands in the snakes have been differentiated into organs for the 

 formation of extremely powerful poisons. These are of two main classes : some, 

 such as that of the Australian black snake (Pseiidechis porphyriaca), investigated 

 by C. J. Martin (1894), act on the blood, causing intra vascular clotting; some of 

 this class also contain hsemolytic substances. The other class, typified by the 

 Cobra, act on the central nervous system, causing paralysis of respiration (Laiult, 

 1903). Further details may be found in the papers quoted as also in those of 

 Fraser and Gunn (1909 and 1912). 



The meaning of the enormous variety of toxic and other alkaloids produced by 

 plants is very difficult of explanation. It would seem that, if their presence were 

 merely to avoid being eaten by animals, one or two distasteful substances would 

 have sufficed. It may be that they are in many cases, as it were, accidental by- 

 products of metabolism, although the possibility of some hitherto unknown action 

 on nutritive processes must not be forgotten. 



Hirudin. It has long been known that the blood sucked by the leech into 

 its alimentary canal remains liquid, and it was found by Haycraft (1884) that there 

 are certain unicellular glands, close to the mouth of these animals, which secrete 

 a substance which has the power of depriving blood of its coagulating property. 

 This it does both when injected into the blood vessels of a living animal, or when 

 added to the blood in vitro. The leech appears to benefit from the arrangement 

 in two ways : there is no risk of blocking of the fine incision made by its teeth in 

 the skin of the animal attacked and from which it is sucking blood, and the blood 

 in its alimentary canal is naturally more accessible to the action of enzymes than 

 if solidified. 



The substance, which can be obtained in solution by extracting the heads of 

 the leeches with water, either directly, as in Abel's method (1914), or after 

 drying with alcohol, as in that used by Haycraft, has been of great service in 

 experiments where it is necessary to collect blood from the veins of organs or to 

 measure its rate of flow. This applies both to organs in situ and to artificial 

 perfusions. The blood rendered non-coagulable by this means appears to be 

 more normal than if defibrinated by whipping ; rabbits are killed by injection of 



