May, 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



429 



estimating the amount of nitrogen in the various pro- 

 ducts separated at the different stages, there is from the 

 very earliest period a consideraljlc discrepancy when 

 this is compared with the amount of nitrogen in the 

 original proteid. 



This must mean that substances are formed which 

 are not detected and isolated by the methods made use 

 of for this purpose, and that a large proportion of 

 soluble nitrogenous products, not giving the biuret re- 

 action, are formed. Pfaundlcr succeeded in showing 

 that these products, if submitted to the action of acid, 

 gave rise to amino-acids, which could then be detected 

 in the solution. These products are, then, similar to 

 the polypeptide now isolated. 



.'\nother point that has been clearly established is 

 that these amino-acids vary greatly in the ease with 

 which they are split off. Leucin and tyrosin are the two 

 first amino-acids to appear and separate at a compara- 

 tively early stage of digestion. It is true that these 

 acids are more easily detected than many of the others, 

 but careful search has failed to detect the presence of 

 other acids at an equall}' early stage, and in this con- 

 nection it is interesting to note that the synthetic pep- 

 tides built up from these acids are the ones which were 

 found to be attacked bv enzymes. 



These soluble polypeptides possibly form a kind of 

 resistant nucleus in the proteid molecule. The view 

 that a resistant nucleus remains after various simpler 

 groups have been split off has long been held; its nature 

 has iDeen much debated, and is still unsettled, though 

 the theory that it is a polypeptide-like body finds con- 

 siderable support. 



We may regard the proteid molecule as built up, 

 therefore, of a large number of amino-acids, the struc- 

 ture of which suffers very little change in this incorpora- 

 tion, so that these acids are again readily split off. 

 The nature of this linking is probably that indicated by 

 Emil Fischer and described above." Certain of these 

 groups appear to offer a more vulnerable point of at- 

 tack on which the hydrolysing agent seizes to begin 

 the demolition of the molecule. This demolition only 

 can proceed gradually, resistance being offered at every 

 stage. 



The great problem of the method of absorption of 

 proteids from the alimentary canal, of which so little is 

 known and which is yet of such vital importancje, is 

 intimately bound up with the question of proteid chemis- 

 try. We can trace the digestion of the proteid in the 

 alimentary canal and detect there albumose and pep- 

 tone, but in the blood vessel which carries away the 

 products of digestion neither albumose nor peptone can 

 with certainty be detected, and we can detect no in- 

 crease in its proteids as the blood leaves the .ilimentary 

 canal after a meal. The detection of small quantities 

 of albumo.se and peptone in the blood would not be 

 easy, and a slight increa.se of proteid might readily 

 escape obser\ation, for the estimation in such a dilute 

 solution does not permit of extreme accuracy. On the 

 other hand since the breaking down of the proteid is 

 more complete than was at one time supposed, the 

 nitrogenous matter may be absorbed in the form of 

 .some of the.se simpler soluble substances, which have 

 lor so long remained undetected; indet'd, it is found 

 that peptides and amino-acids administered as food, 

 lead ti) an increasetl excretion of urea. 



Certain feeding experiments have Ixx-n carried out 

 with the object of throwing light on this most difficult 

 and 111 )st fundamental of problems. Li.wi showed that 

 nitrogenous equilibrium mav be maintained in do<.s fed 

 with the crystalline cleavage products resulting'' from 



the pancreatic digestion of proteids, which no longer 

 give the biuret reaction. The experiments of Abder- 

 halden do not fully support this ; he found that 

 casein and the products of pancreatic proteolysis of 

 casein were equally efficacious as foods; this solution, 

 however, still gave a biuret reaction, and if the diges- 

 tion were carried further by treating the proteid with 

 acid, death resulted if the feeding was continued for 

 long with such a solution. Further development of 

 such work is desirable, for it would be of the very 

 greatest importance if it could be established that the 

 complicated proteid is not an essential food for the 

 maintenance of animal life. 



Now that the synthesis of the simpler carbohydrates 

 is an accomplished fact and that of the simpler proteids 

 has been brought within the region of probability, the 

 old distinction at one time drawn between plant and 

 animal foods loses much of its force. Plants we know 

 can from the simplest materials, carbonic acid and 

 water, manufacture carbohydrate, whilst their nitro- 

 genous food may be supplied to them in the simple 

 form of nitrate or ammonium salt. Animals, on the 

 other hand, require carbohydrate and proteid to be sup- 

 plied ready-made, some living organism having already 

 accomplished the work of elaboration. It is not so 

 very long since these substances seemed almost re- 

 moved from the possibility of synthesis; it was as if they 

 were divided off by barriers, akin to those that were 

 supposed to separate organic and inorganic substances 

 before the first organic compound had been synthesised 

 in Wohler's laboratory. If now it can be shown that 

 it is merely a question of the form in which the simple 

 food is supplied, and that an assortment of the.se com- 

 paratively simple amino-acids will serve as nitrogenous 

 food, the difference between the complexity of plant 

 and animal food becomes of a much lower degree, and 

 the idea of a synthetic laboratory food no longer is to 

 be regarded as an impossibilitv. 



^^^^^^ 



The Work of Radium. 



What is the work that is being done by radium as it 

 continues — for 30,000 yeais or more — to shoot out 

 atoms and electrons? Some attempt to give a concrete 

 illustration of its accomplishment has been made bv M. 

 Holzmuller, in continuation of the calculations made bv 

 Dr. Wien. A milligramme of radium shoots out some 

 29,000,000 negative electrons every second with a speed 

 approximately five-sixths that of light. These are the 

 (i rays. It is also sending out a rays which are particles 

 much more massive, but the speed of which is only one- 

 eighteenth that of light. The amount of work which is 

 thus being done can, of course, only be expressed in 

 "ergs." M. Holzmiiller's calculations take as their 

 starting point that a milligramme of radium bromide is 

 doing \\ork equal to 7^2 ergs a second. But the pure 

 radium in radium bromide is only three-fifths of the 

 whole substance, so that the radium is actuallv doing 

 more work than this; and to cut these calculations down 

 to their smallest possible proportions we arrive ulti- 

 mately at the estimate that a milligramme of radium 

 I)efore it has exhausted all the energy occluded in its 

 atoms will have done some ten billion ergs of work. In 

 other words, it will have done work equal to 100,000 

 kilogrammetres; and, to make the final mathematical 

 reduction, a gramme of radium, which is a very small 

 crumb of material, exhausts in the course of its life an 

 <iiergy ei|ual to work at the rate of one horse-power 

 lor 15 da\s. 



