18   Murder and manslaughter defined

(1) 

(a)  Murder shall be taken to have been committed where the act of the accused, or thing by him omitted to be done, causing the death charged, was done or omitted with reckless indifference to human life, or with intent to kill or inflict grievous bodily harm upon some person, or done in an attempt to commit, or during or immediately after the commission, by the accused, or some accomplice with him, of a crime punishable by penal servitude for life or for 25 years.

(b)  Every other punishable homicide shall be taken to be manslaughter.

(2) 

(a)  No act or omission which was not malicious, or for which the accused had lawful cause or excuse, shall be within this section.

(b)  No punishment or forfeiture shall be incurred by any person who kills another by misfortune only, or in his own defence.