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 1 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 5G°, 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 b 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 intravascular clotting 
in all )ino 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., Joum. Physiol., Cambridge and London, vol. xiv. p. 3-17 ; xviii. 
p. 5-1 ; Pickering and Halliburton, ibid., vol. xviii. p. 285. More recently Pickering lias 
succeeded in making several new proteiddike colloids (Proc. Pay. Soc. London, 1896, 
vol. lx. 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 {Joum. PltysioL, Cambridge and London, 
1896, vol. xx. p. 310). 
