. Diseases of metabolism and of the blood, animal parasites, toxicology. Constitutional diseases; Metabolism; Blood; Medical parasitology; Poisons. 280 BLOOD AND BLOOD EXAMINATION mits the sunlight to penetrate this for a definite time. The degree of black- ening which the paper shows under the blood layer is compared with a stand- ard scale, and then the hemoglobin is read from a table which has been obtained empirically. In quite a series of investigations I have compared the results obtained with the apparatus of Gowers and Gaertner and have found reasonable Fig. 12.—Hemophotog
. Diseases of metabolism and of the blood, animal parasites, toxicology. Constitutional diseases; Metabolism; Blood; Medical parasitology; Poisons. 280 BLOOD AND BLOOD EXAMINATION mits the sunlight to penetrate this for a definite time. The degree of black- ening which the paper shows under the blood layer is compared with a stand- ard scale, and then the hemoglobin is read from a table which has been obtained empirically. In quite a series of investigations I have compared the results obtained with the apparatus of Gowers and Gaertner and have found reasonable Fig. 12.—Hemophotogeaph. (After Gaertner.) ' =^>m Fig. 13.—Hemophotograph. (After Gaertner.) When by the aid of some of these instruments a result has been obtained, it must always be borne in mind that no exact test has been made, that, on the contrary, all sorts of errors may be present. Those which are due to the imperfections of the instrument I have already pointed out; and we must always assume 5 to 10 per cent, of errors in the examination of a definite drop of blood, even although we are quite expert in the examination; with the novice this percentage may be much greater. Unfortunately, it is impos- sible by the use of more exact so-called physiologic methods to avoid these errors in the estimation of hemoglobin, partly because the methods are com- plicated, and partly because they require too large amounts of blood, and, therefore, cannot be utilized in practice. To these errors, which are, however, due to the methods or instruments, still others must be added which are due to a certain changeability in the blood itself. It is well known that the most varied influences may change the caliber of the blood-vessels, by stimulating the vaso-dilators or the vaso- constrictors; for example, light, heat, cold, muscular activity, etc. Accord- ing to the caliber of the vessels—of course within certain narrow limits— the number of corpuscles in the capillary blood will vary, and with th
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