Yet another explanation is called for. Beyond the exposition of those general truths constituting the Principles of Biology as commonly accepted, the original edition of this work contained sundry views for which biological opinion did not furnish any authority. Some of these have since obtained a certain currency; either in their original forms or in modified forms. Misinterpretations are likely to result. Readers who have met with them in other works may, in the absence of warning, suppose, to my disadvantage, that I have adopted them without acknowledgment. Hence it must be understood that where no indication to the contrary is given the substance is unchanged. Beyond the corrections which have been made in the original text, there are, in some cases, additions to the evidence or amplifications of the argument; but in all sections not marked as new, the essential ideas set forth are the same as they were in the original edition of 1864.
The aim of this work is to set forth the general truths of Biology, as illustrative of, and as interpreted by, the laws of Evolution: the special truths being introduced only so far as is needful for elucidation of the general truths.
For aid in executing it, I owe many thanks to Prof. Huxley and Dr. Hooker. They have supplied me with information where my own was deficient;[1] and, in looking through the proof-sheets, have pointed out errors of detail into which I had fallen. By having kindly rendered me this valuable assistance, they must not, however, be held committed to any of the enunciated doctrines that are not among the recognized truths of Biology.
The successive instalments which compose this volume, were issued to the subscribers at the following dates:--No. 7 (pp. 1-80) in January, 1863; No. 8 (pp. 81-160) in April, 1863; No. 9 (pp. 161-240) in July, 1863; No. 10 (pp. 241-320) in January, 1864; No. 11 (pp. 321-400) in May, 1864; and No. 12 (pp. 401-476) in October, 1864.
I. ORGANIC MATTER 3 II. THE ACTIONS OF FORCES ON ORGANIC MATTER 27 III. THE RE-ACTIONS OF ORGANIC MATTER ON FORCES 45 III^A. METABOLISM 62 IV. PROXIMATE CONCEPTION OF LIFE 78 V. THE CORRESPONDENCE BETWEEN LIFE AND ITS CIRCUMSTANCES 91 VI. THE DEGREE OF LIFE VARIES AS THE DEGREE OF 101 CORRESPONDENCE VI^A. THE DYNAMIC ELEMENT IN LIFE 111 VII. THE SCOPE OF BIOLOGY 124