170 SCIENCE PROGRESS 
biogens in the form of an NO, grouping attached to a benzene 
ring, and that one atom of oxygen from the NO, oxidises the 
—CHO or —CHOH groups of the carbohydrate molecule to 
CO, and water. 
The hypothesis that the respiratory processes of tissues are 
carried out by non-nitrogenous side chains is borne out by some 
curious and unexpected results obtained by the writer. It was 
found that when recently excised mammalian kidneys were per- 
fused with saline solution, the protoplasm of the tissues was in 
a state of such extreme instability that it was liable to undergo 
sudden disintegration, whereby a good deal of proteid, proteid 
decomposition products and intracellular ferments (such as 
erepsin) passed out into solution. In various experiments 
carried out under normal conditions, from g to 17 per cent. 
of the total proteids present in the kidney tissues were washed 
out during the course of an eleven-hour perfusion, and yet the 
respiratory powers of these kidneys were just as great as those 
of other kidneys in which there had been little or no tissue 
disintegration. 
The carbohydrate-like nature of the side chains receives 
support from the above-mentioned facts concerning lactic acid 
formation in the tissues. We know that sugars are converted 
into lactic acid not only by the action of various bacteria, but 
also by intracellular enzymes such as the lactacidase enzyme of 
the expressed juice of yeast (Buchner and Meisenheimer). Such 
lactic acid formation may be a normal stage in the oxidation of 
the carbohydrate-like chains to CO,, or it may be an exceptional 
one, occurring but seldom unless the conditions of oxidation in 
the tissues are deficient. If the —CHOH groupings of the 
carbohydrate side chains are oxidised one at a time, they would 
presumably pass through an aldehyde stage first. That an 
aldehyde stage does occur at some point or other in the course 
of tissue respiration, seems to be borne out by some observations 
of the writer. Thus it was found that if an excised mammalian 
kidney were perfused with saline containing ‘1 to ‘2 per cent. of 
hydrocyanic acid, its gaseous metabolism, when estimated shortly 
after in the usual way by perfusion with normal oxygenated 
saline, was at a minimum at first, but that it steadily increased 
for the next eleven hours. During the perfusion, small quantities 
of HCN broke away from the tissues, and hence it was surmised 
that this HCN was bound up to —CHO groups so as to form 
