nothing to do with organic matter, either dead or alive. The question is, whether a saline solution which will sustain bacterial life, or which enters into the composition of bacteria, will rearrange its atoms, or can by any means short of the introduction of living or once-living matter be made to rearrange them, so as to originate the protoplasm of bacterium. Albumen, fat, infusions of mutton, turnip, hay, &c., are either ready-made protoplasm, or else contain protoplasm. But can we put together life by putting together the chemical constituents of the matter of life? Until we can we are not its creators.

In his "Fragments of Science," Professor Tyndall writes: "Holding as I do the nebular hypothesis, I am logically bound to deduce the life of the world from forces inherent in the nebula. With this view . . . it seemed but fair to associate the reasons which cause me to conclude that every attempt made in our day to generate life independently of antecedent life has utterly broken down." If Professor Tyndall literally means forces, I see no logical objection why these forces should not be manipulated as we manipulate other natural forces. If he means that life was inherent in the nebula, it is not easy to understand what conception of it is compatible with conditions implied by the nebular hypothesis.

As to the theological consequences, the making of a bacterium is only more significant than the making of a diamond, in that a living organism is more interesting than a crystal. Under no conceivable circumstances can we ever know more than how to assemble the appropriate conditions-how to combine the already fitted materials, the congress of which is essential to life.

The true and vast importance of the subject lies in its relation to surgery and infectious diseases. The discoveries of Dr. Tyndall and of Dr. Budd as to the contents of the air, and the practical application of these discoveries by Mr. Lister, have enabled the surgeon to perform hundreds of operations which, before the antiseptic treatment, were

far oftener fatal than they are now successful. If also it be true that one-seventh of the human race die of tubercle, and tubercle is due to the presence of bacilli in the blood, the investigations of Dr. Koch of Berlin and of M. Pasteur have been productive of results the extraordinary value of which it is beyond our power yet to estimate.

LETTER VI.

WE must for the present content ourselves with taking life as ready-made. We can, however, begin where, to our very limited powers of penetration, seems to be its beginning the undifferentiated structureless germ.

The most systematic account of germ-development yet offered is to be found in Professor Häckel's two famous books, the "History of Creation" and the "Evolution of Man." Since the publication of these, Mr. F. M. Balfour's great work on "Comparative Embryology," while adding enormously to the stock of facts, compels us to receive some of Professor Häckel's deductions with caution. Of course Professor Häckel's own observations are not to be contested; and for the superficial notice here required no better text-books are needed than his.

cess.

Professor Häckel's theory is that, all living things are derived from MONERA; and that monera themselves are constantly coming into being by a simple and natural pro"The entire body of one of these monera during life is nothing more than a shapeless, mobile, little lump of mucus or slime, consisting of an albuminous combination of carbon.") To the naked eye the moneron is about the size of a pin's head. It wriggles about in the liveliest manner, projecting and withdrawing little filaments like arms and legs from every side. It feeds upon atoms which accidentally become imbedded in its surface. The digestion of food-particles by absorption and simple diffusion through the mass, shows its structureless character.

1 History of Creation, translated by Professor E. Ray Lankester.

Finally, it propagates itself by self-division as soon as it has outgrown its normal size.

This description of the moneron would almost serve for that of the cell. "Originally every organic cell is only a single globule of mucus, like a moneron, but differing from it in the fact that the homogeneous albuminous substance has separated itself into two different parts, a firmer albuminous body, the cell-kernel (nucleus), and an external softer albuminous body, the cell-substance or body (protoplasma)." The term "cell," therefore, does not always mean a little bladder filled with viscid fluid, as was formerly supposed to be the case; for while some cells have limiting membranes, others are without. Plant-cells are, for the main part, encased; but most of the animal-cells -those, for instance, in our own bodies, such as the colourless corpuscles in the blood—are naked specks of protoplasm with a nucleus.

Professor Häckel accounts for the formation of the kernel "by the condensation of the innermost central part of the albumen;" the naked cell puts on the cellmembrane, likewise, in a quite simple physical manner, "either as a chemical deposit or as a physical condensation in the uppermost stratum of the mass, or as a secretion."

Having got from the moneron to the cell, we must next speak of the "cell-theory." Goethe had stated that, every living being is not a unity, but a plurality. Even when it appears as an individual, it is the reunion of beings living and existing in themselves," &c. About thirty years ago Schleiden and Schwann confirmed this statement, establishing the doctrine that the tissues of every plant and animal are built up of cells. The language of Goethe might now be used by Dr. Virchow or Claude Bernard; and in the words of Häckel, "Every organic cell is to a certain degree an independent organism, a so-called 'elementary organism,' or an 'individual of the first order.' Every higher organism is, in a measure, a society or a state

VOL. I.

S

of such variously shaped elementary individuals, variously developed by division of labour."

The metazoon or many-celled organism is but a colony of protozoa or single-celled organisms. How protozoa become metazoa is not by any means so clear as Professor Häckel seems to think. The first step must necessarily be one of reproduction. Amongst the protozoa there are three ways in which this is accomplished: (1) fission, (2) budding or gemmation, (3) spore formation. Fission takes place, as in the moneron, by self-division, "the nucleus. when present becoming divided simultaneously with the cell-body." "The process of budding differs mainly from simple fission in the fact that the two organisms produced are dissimilar in size." Spore formation consists "in the breaking up of the organisms into a number . . . of portions, each of which eventually develops into an organism like the parent form."1

The mere multiplication of the protozoa does not, however, explain the development of the metazoa. These "all originate from the coalescence of two cells, the ovum and spermatozoon. The coalesced product of these cells-the fertilised ovum-then undergoes a process known as the segmentation, in the course of which it becomes divided in typical cases into a number of uniform cells."2 The process of reproduction here, then, is no longer asexual, but sexual; and we pass from ordinary unicellular forms to a special unicellular form-the egg. What is this egg? "Every ovum," says Mr. Balfour, "has the character of a simple cell. It is formed of a mass of naked protoplasm, containing in its interior a nucleus, within which there is a nucleolus." "Every primitive egg," says Häckel, "being originally an entirely simple, somewhat round, moving, naked cell, possessing no membrane, and consisting only of the nucleus and protoplasm." 3 In spite of the ova being "entirely simple," there appear 2 Comparative Embryology, vol. ii. p. 274. 3 Evolution of Man.

1 Balfour.