January, 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS 



317 



determining the breeding seasons of many species of 

 mammals and birds, yet the periods of drought and 

 ivet are so local, and determined to such an extent by the 

 geographical conditions of the country, that they need 

 not be considered in a paper dealing with the subject 

 so broadly as the present one. 



We are, therefore, not likely to find in the tropics 

 great differences of colour, since any climatic change 

 that may exist will tend not to coincide with the breed- 

 ing season, and the latter will be spread over the greater 

 part of the year. 



From these reasons, therefore, it will be evident that 

 the life of an animal will run much more evenly so far 

 as its metabolism is concerned, and, food and tempera- 

 ture being favourable to a high state of vigour, we 

 should expect to find animals deeply coloured and re- 

 maining so throughout the year. 



So'Uie animals, however, will be so weak that thev 

 can only exist where the conditions of life are most 

 favourable, so that, although living in the tropics, their 

 vigour will be low. Such animals, therefore, according 

 to my argument, should be white or pale coloured, and 

 restricted to the tropics, while the brighter-coloured 

 tropical animals should be found to have a much w'ider 

 range, the majority decreasing in colour as they spread 

 north or south. 



Of these brighter animals the tiger and leopard afford 

 good examples. The buffalo of India is black, but in 

 Assam a light variety is found, and the more northern 

 species of Bos are found to be lighter in colour. The 

 squirrels, another brightly-coloured group, are, like the 

 oxen, cosmopolitan, shading through brown to grey in 

 the northern regions. 



White or grey tropical mammals are \erv scarce, 

 but we may notice the bamboo rat (R/iizomys 

 snmalrensis), which is dirty white in colour and does not 

 range north of Burmah. R. pruinosus, a rather darker 

 species, ranges as far north as Assam, while R. badius 

 and R. sinensis, both dark brown species, range from 

 the south as far north as Bhutan, Nepal, and even 

 Thibet. 



.'\s regards the liirds, w x- may notice the kingfishers 

 and rollers, typical tropical families, which range to 

 more northern climates. 



The parrots, which by the same process of reasoning 

 one would expect to find in more temperate zones, only 

 extend to a limited extent. This is probably due to 

 two causes : — 



(i.) Their sedentar\- habits. 



(2.) The fact that many of them are not as brighth' 

 pigmented as they appear on the surface, 

 the predominating pigment being yellow. 



On the other hand, many of them are perfectly hardv, 

 and sl:md our climate out of doors well, so that probablv 

 their sedentary habits have been no small factor in re- 

 strictmg their range. Humming birds also range far 

 toi the north, but have to- retreat before the winter, pro- 

 bably from lack of food, while the sunbirds of India 

 are probably restricted l)y the Himalayas. The 

 riiasi:niichr. are another example of hrigiit-coloured 

 tropical groups extending northwards. 



Dull-coloured tropical birds (not counting those from 

 temperate regions that have migrated to the tropics) 

 are not numerous. 



The hoatzin (O pislhocoiiiiis) is, howexer, a good ex- 

 ample of a dull-coloured tropical bird, which, as we 

 might expect, wc find restricted to the tropics, while 

 the bell birds (Chiasniorhynclins) form another good 

 example. 



{CnntillUi'll.) 



Ths Venom of Spiders. 



By C. Ai.NswoRTH 'Mitchell, B.A. (Oxo.v.), F.I.C. 



{Cuntinued from page 299.) 



The modern conception of toxines is based on 

 lihrlich's "side-chain" theory, according to which a 

 to'xine is a very unstable body, whose molecule may be 

 represented as containing different unsaturated groups. 

 One of these is termed the liapioplicrc group, and it is 

 that wliich combines with corresponding groups 

 (receptors) in the attacked cells and enables the active 

 or ioxophcre group to> do' its work. If there are no 

 corresponding groups in the blood of the animal the 

 toxine simply circulates inertly and finally disappears. 

 A striking instance of this is seen in the effect of 

 tetanus (lock-jaw) poison upon the alligator, for al- 

 though the reptile itself is proof against the action of 

 tetanus, its blood becomes toxic and will infect a sus- 

 ceptible animal, i.e., one whose blood contains suitable 

 receptors for the toxine. 



In like manner the hedgehog is refractory to snake 

 venom, and also' tO' spider venom, and its partial in- 

 susceptibility must be attributed to a lack of receptors, 

 for the blood of a hedgehog that has been bitten 

 becomes highly venomous. 



It is further assumed in Ehrlich's theory that " side 

 chains " are generated within the animal, to replace 

 those of the cells fixed by the toxine, and these, being 

 formed in excess, circulate in a free state in the blood 

 and form the specific immune substance or antitoxine. 



Now, spider venom answers all the requirements of 

 a toxine, as defined bv Dr. Ehrlich. It is unstable, and 

 produces an antitoxine which is capable of neutralis- 

 ing its action when mixed with it in the right propor- 

 tion. It resembles snake venom in possessing more 

 than one active principle. In snake venom there is one 

 toxine which acts upon the nervous system, a second 

 acting Upon the cell walls, and a third, termed a 

 Iicfm.iilvsiiH\ which dissolves the corpuscles of the blood, 

 .Similarly, in spider venom there is one active principle, 

 which acts upon the nervous system and heart, and 

 another, a hremolysine, with a solvent action upon the 

 red blood corpuscles. 



This hamiolysine has recently been separated from 

 the common garden spider by Dr, Sachs, who terms 

 it aracluinlysine. It has a very energetic action upon 

 washed blood corpuscles. Those of the rabbit, rat, and 

 mouse .are rapidly dissolved, while human blood cor- 

 puscles are less susceptible, and those of the guinea 

 pig, sheep, horse and ox absolutely refractory. The 

 blood corpuscles of young chickens are at first quite 

 refractory, evidently from a lack of rcce ptrrs to combine 

 with the haptofihore group of the toxine, but as the bird 

 growls older its corpuscles become more susceptible, 

 until after about a month they attain the normal sus- 

 ceptibility of the hen, Dr, Sachs also succeeded in pro- 

 ducing an antitoxine, anli-arachnol ysinc, to this toxine 

 by inoculating animals with gradually increasing 

 doses. The serum of the animal thus immunised was 

 very active, and when mixed with freshly extracted 

 venom neutralised both its toxic and its haemolytic 

 action. 



There is thus no doubt about the existence of pow- 

 erful toxines in the various species of lathrodcctes and 

 in the garden spider, and possibly in Chiracanthium 

 nutrix, a South European species, and the reason why 

 the bite of these is sometimes insignificant is that the 



