^{page 173 note 1} Royal Commission on Sewage Disposal; Fourth Report; Vol. III; Reports by Dr Houston on Bacteriological Investigations.

^{page 179 note 1} Negative 100 c.c.; +100, −10 c.c.; +10, −1 c.c.; +1, −.1 c.c.; +.1, −.01 c.c.; +.01, -.001; +.001, -001; +0001, −.00001; +.00001. First, second, third, fourth, fifth, sixth, seventh, eighth, and ninth classes respectively. It is obvious that these classes may be subdivided further, but whether or not this is desirable at present is a moot point. For example, we may subdivide the second class according to whether a positive result is yielded with 90, 80, 70, 60, 50, 40, 30, or 20 c.c. of the sample. Such subdivision might be expressed by the term sub-class, 1, 2, 3, 4, 5, 6, 7, 8, or 9 respectively. The same principle applies to the other classes.

^{page 179 note 2} In the sense indicated here the topographical method theoretically is mainly speculative in character. But having regard to the breadth of its operations, it may be and indeed is actually of signal and indispensable value in practice.

^{page 179 note 3} The chemical method is a definite and extremely accurate method, and although indirect in character, may, within certain limits and in certain directions, yield most valuable results.

^{page 179 note 4} The bacteriological method is direct qua numerical estimation of intestinal microbes, but indirect as regards disease-producing bacteria. Although seemingly the best method, and extremely delicate, it is nevertheless to be thought of as of relative, not absolute, value.

^{page 180 note 1} It is essential to note that in my detailed report to the Commission full details are given in each and every case of the biological characters of the coli-like microbes isolated in pure culture from both the waters and the oysters. It may be said, however, that the samples of Helford water and oysters (as well as the samples of Penryn water and oysters) were found to contain typical B. coli (on the basis of the tests employed) in greater or less number. The matter is largely one of proportion.

^{page 185 note 1} This average has been used generally as a convenient basis for calculating the relation between the number of bacteria per c.c. in the oyster and the water over the oyster layings. It is, however, an under-estimate of the bulk of many oysters. It must be remembered that the bacteria are not uniformly distributed within the contents of the oyster shell. No doubt the liquor, alimentary tract and perhaps the gills harbour most of the microbes, and the tissue of the body of the oyster may be, relatively speaking, sterile.

^{page 190 note 1} According to the tentative standard of a negative result with 1 c.c. (see Division III.), all the foregoing samples would be passed, and all the following samples rejected bacteriologically. That is, if the numerical results, as regards B. coli and coli-like microbes, be considered independently of the biological attributes of such microbes.

^{page 193 note 1} It must, be understood that throughout this article no personal responsibility is incurred for topographical expressions of opinion of opinion as regards the purity or otherwise of oyster layings. The rule has been to accept the opinions of the highest authority on the subject, as if they were final, for the purposes of comparison with the bacteriological results.

^{page 193 note 2} Within the limits of this article it is impossible to consider the “modifications of test readings” suggested in my detailed report to the Commission. It may be said, however, that the samples both of water and of oysters obtained from these layings occasionally, if not uniformly, contained typical B. coli (on the basis of the tests employed) in greater or less number. The matter is largely one of proportion.

^{page 195 note 1} It must be understood, definitely, that I have not, as regards any of the layings, selected oysters from separate batches, so as to make up a total of ten oysters, but have chosen the particular batch of ten oysters out of a series of batches of ten oysters yielding the most typical B. coli.

^{page 199 note 1} “On the value of tests for bacteria of specific types as an index of pollution,” by Messrs Clark and Gage. From the Thirty-fourth Annual Report of the State Board of Health for Massachusetts for 1902.