Heavy responsibility lies upon the Mohel to carry out every case strictly in accord with the lessons of surgical cleanliness. _Surgical Cleanliness_ begins where ordinary cleanliness leaves off. Its object is to destroy certain minute particles of matter which are invisible to the naked eye, but which are _living organisms of a vegetable nature_, able to grow very luxuriantly in blood, and wound discharges. Here they produce a poison which gets absorbed into the body, causing serious symptoms of disease; or they themselves enter the blood stream and circulate in it with even more disastrous results. These organisms can be observed under the microscope, but can only be seen by the naked eye when growing together in colonies after being planted in such substances as gelatine or broth, or on the surface of a slice of potato. They correspond exactly to the growth of _mould or fungus_ on stale cheese or meat, or to the growth of yeast in fermenting grape juice. When seen separately under the microscope, or when growing in the mass they possess very distinct characters so that the expert is able to distinguish the one from the other, with the same confidence as a pear may be distinguished from a fig. A large number of diseases is due to the growth in the body of certain of these organisms, and in many diseases we can be sure of always finding the particular one responsible for the condition, either in the blood or in the discharges from the body. This is notably the case in Consumption, Typhoid Fever, and Malarial Fever. We often know how the organism has obtained entrance into the body; it may be either by the lungs or the stomach, or in other words through air or through food. We are however only concerned just now with the _organisms which enter the body by means of an open wound_. These nearly all belong to one class--_micro-cocci_. They are minute round bodies about 1/25000 inch in diameter. They possess the peculiarity of growing together in clusters like grapes, or in chains. They are responsible for the diseased conditions of wounds which delay healing, for inflammation around wounds and for the general blood-poisoning which may result. These organisms are very abundant in the dust of rooms, on dirty clothes and unclean general surroundings, and there can be no doubt that everybody is often infected by them. But fortunately disease results only rarely, because there are special powers resident in the vital tissues which enable them successfully to resist the poisonous effects of these organisms. There are however certain circumstances in which they are liable to be more harmful than in others. _1_) _When they are absorbed in especially large numbers._ _2_) _When absorbed in an especially active state._ _3_) _When the body is in a condition of ill-health from whatever cause._ _4_) _In the presence of cold._