Crimes against persons are not always as easy to classify and understand as crimes against property. These acts are so numerous and come from so many different emotions and motives, that often the cause is obscure and the explanation not easy to find. Still here, as everywhere in Nature, nothing can happen without a cause, and even where limited knowledge does its best and cannot find causes, our recognition of the connection between cause and effect and the all-inclusiveness of law can leave no doubt that complete knowledge would bring complete understanding.  
It is always to be borne in mind in considering this class of crimes that the motive power of life is not reason but instinct. If men lived by reason the race would not survive. The primal things that preserve the race, the hunger for food, drink, sex, are instinctive and not only are not awakened or satisfied by reason, but oftentimes in violation of it. Nature, first of all, sees to the preservation of the species, and acts in a broad way that life may not perish. Nature knows nothing about right and wrong in the sense in which man uses these words. All of our moral conceptions are purely of social origin and hence not instinctive in human life, and are forever giving way to the instincts on which Nature depends. The preservation of life has called for the emotions of hate, fear and love, among the other emotions that move men. The animal fears danger and runs away, and thus life is preserved. The weaker animal is almost entirely dependent for life upon his fear. He is sometimes afraid when there is no danger, but without fear he would be destroyed. Sometimes the animal hates and kills and thus preserves himself. The love of offspring is the cause of the care bestowed upon it which preserves its life. The herd instinct in animal species develops packs and clans and tribes and states. Man is the heir to all the past, and the instincts and emotions of the primitive animal are strong in his being. These may have been strengthened or diluted as the ages have come and gone, but the same instincts furnish the motive power for all his acts. Man fears and hates, and runs or kills and saves his life. He loves, and preserves his offspring.
 
Man sees an object. Instinctively he may fear it or he may hate it. He may run from it or destroy it. He gathers impressions through his senses. The nerves carry them to the brain. He comes to fear certain persons and things, to hate certain other persons or things, and to love still others. If the hatred is strong enough or the danger great enough or the desire sufficient, he may kill. Whether he plans the method or deliberates upon the act can make no difference. He is prompted by the instinct, and the reflection simply means the consideration of reasons for and against, or the reaching of inhibitions. If he acts, it is one of the primal emotions that causes the act. He is the "machine" through which certain emotions find their path and do their work. Infinite are the causes and circumstances that give rise to an emotion strong enough to take human life.
 
Killings which result from a sudden passion are easily understood. Everyone has been overwhelmed by rage, where reason and judgment and all acquired restraints are entirely submerged. The primitive man with his primitive emotion reasserts himself. It is mainly accident or the lack of some particular circumstance that prevents a murder. Of course some people are overwhelmed more easily than others. Some natures are less stable, some nervous systems less perfect, and the built up barriers are weaker. The whole result of stimuli is determined by the strength of the feeling acting upon the machine. Such a person is not ordinarily dangerous to the community. The act itself would generally assure that it could never happen again. Some killings, however, are more deliberate. They are preceded by a settled hatred which preys upon the mind and fights against the preventive influences that training and habit have formed. Under a certain combination of circumstances these restrictions are swept aside and the emotions have their way.
 
There are, of course, certain broad classifications of homicides. A considerable number, perhaps more than any other, come through the commission of robbery, burglary and larceny. In the midst of the act the offender is caught, and kills in an effort to escape. These murders fall under the heading of property crimes; the cause is the same, and the rules governing them are the same. Th............