=280.= Modern biologists deal with this subject with the minuteness of detail of which the microscope is the instrument, and with the wealth of illustration which results from the incessant accumulation of ascertained facts. But they are perhaps open to the criticism that where they reach the borders of their own science, they are apt to introduce references to the sciences of chemistry and physics as explaining all difficulties, even in regions to which these sciences do not apply. The following account is taken from one of the most eminent of them: ‘Hertwig discovered that the one essential occurrence in impregnation is the coalescence of the two sexual cells and their nuclei. Of the millions of male spermatozoa which swarm round a female egg-cell, only one forces its way into its plasmic substance. The nuclei of the two cells are drawn together by a mysterious force which we conceive as a _chemical sense-activity akin to smell_, approach each other and melt into one. So there arises through the sensitiveness of the two sexual nuclei, _as a result of erotic chemotropism_, a new cell which unites the inherited capacities of both parents; the spermatozoon contributes the paternal, the egg-cell the maternal characteristics to the primary-cell, from which the child is developed[80].’ In another passage the same author sums up his results in bold language from which all qualifications and admissions of imperfect knowledge have disappeared: ‘Physiology has proved that all _the phenomena of life may be reduced to chemical and physical processes_. The cell-theory has shown us that all the complicated phenomena of the life of the higher plants and animals may be deduced from the simple physico-chemical processes in the elementary organism of the microscopic cells, and the material basis of them is the plasma of the cell-body[81].’ [Sidenote: Their inadequacy.]