Mr. V. A. Clark, as a student in horticulture inthe University of Vermont, first undertook a criticalexamination of Nägeli's Mechanico-PhysiologicalTheory of Evolution as a part of his regular juniorwork. After a half year's study and the preparationof a short thesis, Mr. Clark had become so farintimate with Nägeli's work as to make it seembest for him to continue the study through hissenior year. This study involved extended translationsfrom the text, including Nägeli's Summary,which, considering its difficult accessibility to Americanstudents, has been chosen for publication. Thework has been done chiefly by Mr. Clark, but hasall been under my immediate supervision, and Ihave given the whole matter a final restudy andrevision. Those who have had any experience withsimilar work will know how impossible it is that allmistakes should have been avoided, and it would bea kindness to the translators if readers would pointout any defects, in order that they may be corrected.
University of Vermont,
July 1, 1898.
[ 1 ]
In this summary I shall in general pursue acourse the reverse of that which my main workfollows.[A]I shall proceed from the primitive, unorganizedcondition of matter and endeavor to showhow organized micellar substance has arisen in it,and how, from this micellar substance, organismswith their manifold properties have arisen. Sincesuch a synthesis of organisms out of known formsof matter and force is still far removed from aconclusion strictly in accord with physical law, theprocess becomes comprehensible and obvious onlyby exact knowledge of the discussion that haspreceded. Although the synthetic method revealsmore clearly the weaknesses of the theory than doanalytic investigations, yet I considered it helpful[ 2 ]to make this presentation in order to give a cleareridea of the mechanico-physiological theory, and atthe same time to test its worth.
When separated and promiscuously moving moleculesof any substance in solution or in a meltedcondition pass into the solid form by reason ofremoval of the causes of separation and motion(warmth or solvent), they arrange themselves intosolid masses impermeable to liquids. These minutebodies grow by accretion, and when molecularforces are permitted to act undisturbed, assume theregular outer form and inner structure of crystals.The number of crystals, their size, changes of formand growth, all depend on external conditions.
Certain organic compounds, among them albumen,are neither soluble, despite their great affinityfor water, nor are they fusible, and hence are producedin the micellar form. These compounds areformed in water, where the molecules that ariseimmediately adjoining each other arrange themselvesinto incipient crystals, or micellæ. Only suchof the molecules as are formed subsequently andcome in contact with a micella contribute to itsincrease in size, while the