| | | | | |(_g_) 0·3 per cent. Na₂CO₃} |White lead | | „ | | 0·5 per cent. NaCl } | | | | | | | | | |(_h_) 0·3 per cent. Na₂CO₃} |Metallic lead | | „ | | 0·5 per cent. NaCl } | | | | +--------------------------------+---------------+------+-----------+ The experiments referred to on p. 18 undoubtedly agree with those of Schicksal. In addition to the presence of peptones, the effect of carbonic acid must be also considered, as increase in solubility in gastric and pancreatic digestions was produced when carbonic acid gas was bubbled through the digest during the period of action. The whole question of solubility of many materials in the fluids of the stomach and intestinal canal requires entire revision, not only as regards lead, but as regards a number of other metals, including arsenic. =The Mechanism of Lead Absorption.=--The final method of absorption of lead particles or lead solution into the animal body remains to be considered. Experimental phagocytosis of lead particles--as, indeed, of any minute particles of substance--suspended in an isotonic solution, may be observed directly under the microscope. Lead particles show no exception to the rule, and white blood-corpuscles in a hanging-drop preparation, made by suspending them in an isotonic salt solution and serum, may be watched englobing particles of lead, and by appropriate means the ingested lead may be afterwards demonstrated. In such an experiment, much of the lead absorbed by the individual corpuscles rapidly loses its property of giving a black precipitate with sulphuretted hydrogen, and has apparently become converted into an organic compound, peptonate or albuminate. In the section devoted to the Chemistry of Lead, it has been noted that the colloidal solutions of lead are not precipitated by sulphuretted hydrogen, and that albuminates and peptonates of lead are presumably of colloidal form. There seems evidence, therefore, that the direct absorption of lead takes place by means of the phagocytes of the body, and that in them it becomes converted into a colloidal form, in which it is probably eliminated through the kidney and intestine, mainly the latter. Further evidence of the englobement of lead particles by amœbic cells may be gained if sections of the intestines of experimental animals are examined; in the lymphoid glands particles of lead may be seen situated in the interior of the walls, and even in the cells. It does not by any means follow that these particles of lead sulphide present in the cells have been formed _in situ_; more probably the lead has been converted into a sulphide in the intestinal lumen itself, and subsequently taken up by the amœbic cells situated in its periphery.