1897-98.] Dr W. G. A. Robertson on Mixed Diets. 
209 
Note on the Effect of Mixed Diet as Regards Salivary 
Digestion. By W. G. Aitchison Robertson, M.D., 
D.Sc., P.R.C.P.E. 
(Read July 4, 1898.) 
The following research was made with the object of determining 
whether the digestion of starch is affected favourably or unfavour- 
ably by its admixture with other articles of food. 
As regards the quantity of saliva secreted per twenty-four hours, 
this is stated to vary from 200 to 1500 grammes. Investigating 
this in my own case I found that the average amount was 400 
grammes. 
Method of Investigation . — Ten grammes of each of the various 
foods as prepared for the table were accurately weighed out, placed 
in a large tube, and heated to 38° C. Two cubic centimetres of 
mixed human saliva were then added. A series of these tubes were 
prepared, and the whole was placed on a water-bath kept at a 
uniform temperature of 38° C. At intervals a tube was removed, 
and the condition of its contents noted. 
Porridge forms a fairly easily digested article of food. The 
greater the dilution of the porridge, however, as with water or 
milk, the greater is its ease of digestion ; in fact, well-made water 
gruel is one of the most easily digested of foods. 
The reason why potatoes are so frequently badly borne by the 
stomach is probably due to the manner in which they are pre- 
pared. If, after being boiled, they are finely powdered, so that 
the saliva can gain ready access to the starch granules, they are 
easily and rapidly digested. On the other hand, when potatoes are 
sent to the table whole, the probability is that they will be 
imperfectly masticated, and swallowed in fragments of more or less 
large size. In such a case the saliva can only act on the outer 
surfaces of the fragments, and the result is a very imperfect 
digestion. Were potatoes prepared properly, I feel sure that they 
might be prescribed as frequently as other farinaceous foods for 
invalids or dyspeptics. 
As regards the digestion of bread, the experiments showed that 
