Perhaps the most serious indictment in connection with its use is the undoubted fact that it induces or initiates rheumatism, and I would like to draw attention to this fact on account of the many cases in which I have seen it produce this effect. In the days of my youth I had frequent opportunities of testing the value of buttermilk, both as a refreshing drink and a dietetic agency with oatmeal-porridge, but its use was invariably accompanied by severe indigestion. In more recent years I have suffered both from colic and indigestion from the use of curdled milk, and therefore did not persevere in its use. On my return from Battle Creek Sanitarium in 1909 I made a persistent attempt to habituate myself to, and, if possible, benefit by its use, and although by employing "Yoghurt" tablets, or capsules, I was able to obviate the indigestion, I repeatedly noticed after a few days - generally the third or fourth day - an exacerbation of a rheumatic pain in my right knee, so severe as to prevent me playing golf. That the pain was not imaginary, nor produced by suggestion, was obvious from the fact that two or three times when I started to take the tablets, in an effort to use them up whilst still active, and entirely forgetful of my previous experience, on the third or fourth day I was again pulled up by rheumatism. This induced me to watch other cases, and I have been able to note attacks of lumbago, sciatica, attacks of muscular rheumatism in various parts of the body, and an occasional effusion into a joint, all produced by its use.

Most physicians are in the habit of counselling their rheumatic patients to keep free from even the slightest suspicion of constipation, knowing by experience how quickly this induces sciatica, lumbago, and fibrositis, and doubtless the constipating tendency of milk has something to do with these untoward results. But there is another factor in the case which is probably of more importance. For many years excess of acidity has been considered as being in some way associated with the production of rheumatism, and lactic acid has been mentioned as the specific agent involved. In the ordinary way it is discovered in the body as one result of indigestion, as also by the metabolic changes in muscle. We know that ammonium is also a product of protein metabolism, and these two substances being carried by the blood to the liver combine to form lactate of ammonia, NH3 + C3H6O3 = NH4C3H5O3, and this in ordinary circumstances is converted into urea. Now, in birds, the liver forms uric acid, and when it is cut out of the circulation lactate of ammonium is excreted instead of uric acid. It would therefore appear, at any rate in birds, that the liver transforms lactate of NH4 into uric acid.

The close association of uric acid, urea, and lactic acid is surely more than a mere coincidence. The molecule of uric acid contains two molecules of urea, combined with an acid containing three atoms of carbon, viz., acrylic acid, which is simply dehydrated ethylidene lactic acid. Uric acid, indeed, has been synthesised by Horbaczewski from trichlorlactic acid and urea.

I make no claim for the recognition of lactic acid as a direct factor in the production of rheumatism - this was sufficiently disproved by Latham in the Croonian Lecture of 1886 - but I do think that in common with many other acids it is an indirect factor. Now, when excessive quantities of lactic acid are formed by fermentation in the alimentary canal, or by feeding with lactic acid bacilli, there is no doubt that these can be absorbed, and it is conceivable that they may interfere in some way with the normal hepatic metabolism. In any case, the constant necessity for neutralising the acid contents of the bowel tends to withdraw alkalis from the system, and lessens the alkaline reaction of the blood, a condition analogous to that which occurs when too much acid fruit is consumed. We have seen that rheumatism is often the direct result of such a practice, and it does not require a very vivid imagination to infer that in a similar manner it may be produced by excess of lactic acid, for, whatever the explanation of the rheumatism may be, it is closely bound up with the ingestion of more acid than the system can tolerate.

It should be carefully noted that curdled milk was introduced by Metchnikoff and his associates, less as an addition to our therapeutical armamentarium than as an item of our daily diet, and from this point of view it may be considered as the most powerful argument in favour of a low-protein diet. If harmful putrefactive organisms only infect the colon when there is a food supply for them in the shape of surplus protein not required by the tissues, then the simplest way to exterminate them is to desist from taking the extra protein. It is surely a work of supererogation, and certainly a waste of energy, to consume the useless extra protein calculated to form dangerous toxins, and at the same time swallow a by no means delectable antidote in the shape of a culture of lactic acid bacilli. But it has yet to be proved that the toxins which are undoubtedly formed are, except when in excess or where the natural protective organs are unable satisfactorily to fulfil their functions, any more dangerous than the irritating acids formed by the antitoxin, and it should be noted that butyric acid bacteria are anaerobic.