THE ATTEMPTED SYNTHESIS OF PROTEIDS. 37 



product is washed with water, and after evaporation in vacuo yields a 

 substance similar in appearance to the colloid (a). 



In all three cases, heavy molecules were formed ; and in all, the 

 result was a colloidal substance, exhibiting many of the properties of 

 proteids. In the case of the first two colloids, there was present not 

 only the amidogen, but also the aromatic radicle. Although the result 

 is not albumin, the resemblance between the physical properties and 

 chemical reactions of proteids and of these synthesised colloids is 

 remarkably close. Pickering l has fully confirmed Grimaux's results, and 

 has added new facts illustrating the points of similarity between them 

 and proteids. 



The chief of these are as follows : 



1. All give the xanthoproteic reaction. 



2. With copper sulphate and caustic potash, a gives a blue-violet ; 

 b, nil ; c, a typical violet coloration, like that given by albumin. 



3. Their solutions do not coagulate on heating in the absence of salt ; 

 if, however, a trace of a soluble barium, strontium, or calcium salt is 

 present, opalescence occurs at 56, and coagulation at 75 C. 



4. The colloids are removed from solution (rising to the surface of 

 the fluid) by saturation with magnesium sulphate, sodium chloride or 

 ammonium sulphate. Here they especially resemble the class of 

 proteids called globulins. 



5. Another resemblance to globulins is seen in their behaviour to a 

 stream of carbonic anhydride, which, in the presence of salts, causes 

 precipitation. The passage of a current of air through the mixture 

 redissolves the precipitate. 



6. The colloid 1) is not digested by pepsin-hydrochloric acid ; a is 

 slightly digested ; c is easily digested, and the solution gives the typical 

 peptone colour, pink, on the addition of copper sulphate and caustic 

 potash. 



7. Any one of the three colloids, when intravenously injected into 

 animals (rabbits, cats, dogs, rats, guinea-pigs) causes extensive intra- 

 vascular coagulation. In a typical experiment death is due to respiratory 

 failure. In this property of the proteid-like colloids, which was dis- 

 covered by Pickering, they closely resemble the nucleo-proteids (see 

 p. 67). The resemblance to the action of the nucleo-proteids extends 

 even to minor points ; for instance, neither cause intra vascular clotting 

 in albino rabbits ; " 2 and in dogs very minute doses indeed, cause a slowing 

 of the rate of coagulation (Wooldridge's negative phase). 



The artificial colloids do not resemble nucleo-proteids in promoting 

 the formation of fibrin in solutions of fibrinogen. 



If nucleo-proteids and these colloids both produce the same effect in 

 the same way, their physiological activity is probably connected with 

 the presence of some radicle common to both. The colloidal condi- 

 tion will not explain the action, since most colloids do not act thus. 



1 Pickering, J. W., Journ. PhysioL, Cambridge and London, vol. xiv. p. 347 ; xviii. 

 p. 54 ; Pickering and Halliburton, ibid., vol. xviii. p. 285. More recently Pickering has 

 succeeded in making several new proteid-like colloids (Proc. Roy. Soc. London, 1896, 

 vol. Ix. p. 337). 



2 This point has been worked out by Pickering also in the case of the Arctic hare. 

 During the albino stage of the animal, neither nucleo-proteids nor synthesised colloids cause 

 intravascular coagulation, but during their pigmented stage intravascular coagulation is 

 produced in the usual way. The change in the external appearance of the animal is thus 

 associated with other changes in its constitution (Journ. PhysioL, Cambridge and London, 

 1896, vol. xx. p. 310). 



